AQA A-Level Maths: Coordinate Geometry — In-Depth Revision Guide (7357)
AQA A-Level Maths: Coordinate Geometry — In-Depth Revision Guide (7357)
Coordinate geometry is one of the most rewarding sections of AQA A-Level Maths (7357) because it sits at the meeting point of algebra and geometry. You take an algebraic equation and turn it into a curve; you take a geometric configuration and reduce it to algebra. Every other pure topic leans on the techniques you build here. If you can manipulate the equation of a circle, parametrise a curve, and reason about tangents and intersections, the rest of the pure course becomes far less intimidating.
This guide is the in-depth companion to the AQA Section C course on coordinate geometry. It covers the spread of content the specification can examine: a review of Year 1 straight lines, the equation and properties of a circle, parametric equations and their calculus, implicit differentiation, curve-sketching strategies, intersection problems, and loci with geometric proof. The Year 1 straight-line and circle work is fair game on Paper 1; the Year 2 parametric and implicit material sits on Paper 2 and Paper 3.
For each topic you will see the core skills, the typical pitfalls, a short worked example, and a link to the full lesson. The aim is to give you a clear map of what AQA can ask, in the order they teach it, so your revision is targeted rather than scattered.
What the AQA 7357 Specification Covers
The AQA 7357 qualification is assessed through three two-hour papers, each worth 100 marks. Paper 1 covers pure from Year 1 plus selected Year 2 pure. Paper 2 covers the remaining pure alongside mechanics, and Paper 3 covers pure alongside statistics. Coordinate geometry is split across the spec: straight lines and circles sit in Section C (Year 1), while parametric equations, parametric calculus and implicit differentiation are Year 2 pure, examined on Paper 2 or Paper 3.
Coordinate geometry is a high-frequency area. Straight-line and circle questions appear almost every series on Paper 1, often as a 6-10 mark structured problem. Parametric and implicit work shows up on Paper 2 or Paper 3, often inside a calculus question. The table below shows the sub-topics and a realistic estimate of the marks weight you can expect across a sitting.
| Topic | Spec Section | Typical paper marks weight |
|---|---|---|
| Straight lines (Year 1 review) | C1 | 4-8 marks (Paper 1) |
| Equation of a circle | C2 | 6-10 marks (Paper 1) |
| Circle properties (tangents, chords, perpendicular bisectors) | C2 | 4-8 marks (Paper 1) |
| Parametric equations introduction | C3 | 4-6 marks (Paper 2/3) |
| Parametric differentiation | C3 / Calculus | 4-8 marks (Paper 2/3) |
| Parametric integration (areas under parametric curves) | C3 / Calculus | 4-6 marks (Paper 2/3) |
| Implicit differentiation | Calculus | 4-8 marks (Paper 2/3) |
| Curve sketching strategies | Across spec | 3-6 marks (any paper) |
| Intersection problems | Across spec | 4-8 marks (any paper) |
| Loci and geometric proof | C2 / Proof | 4-8 marks (Paper 1) |
These weights are estimates based on the spread of typical 7357 papers, not guarantees for any single year. What is reliable is that coordinate geometry techniques recur inside calculus, vectors and trigonometry questions. Mastering this section is high-leverage revision.
Straight Lines Review
Straight-line work is the foundation, and AQA expects it to be automatic by the end of Year 1. The general form y=mx+c gives the gradient m and the y-intercept c directly. The point-gradient form y−y1=m(x−x1) is your default tool when you have a known point and a known gradient — far cleaner than substituting back into y=mx+c. The general form ax+by+c=0 appears on AQA mark schemes as the preferred final answer for many straight-line questions, so always be ready to convert.
The two relationships that drive almost every straight-line question are: parallel lines have equal gradients, and perpendicular lines have gradients whose product is −1. So if a line has gradient m, any perpendicular has gradient −1/m. The midpoint of the segment from (x1,y1) to (x2,y2) is (2x1+x2,2y1+y2), and the distance is (x2−x1)2+(y2−y1)2. These three results — gradient relationships, midpoint and distance — solve the bulk of Year 1 straight-line problems.
A short worked example. Find the equation of the perpendicular bisector of the segment from A(1,2) to B(5,8). The midpoint is M(3,5). The gradient of AB is (8−2)/(5−1)=3/2, so the perpendicular gradient is −2/3. The perpendicular bisector therefore has equation y−5=−32(x−3), which rearranges to 2x+3y=21. Notice how the question reduces to three small steps once you trust the formulas.
A common pitfall is confusing parallel and perpendicular gradient rules under exam pressure. Another is sign slips when rearranging into general form: a sign error in ax+by+c=0 costs the accuracy mark.
For a full refresher with practice questions and worked solutions, see the Straight Lines Review lesson.
Equation of a Circle
The equation of a circle with centre (a,b) and radius r is
(x−a)2+(y−b)2=r2.
This is the form you should always aim for, because the centre and radius are visible at a glance. AQA also expects you to handle the expanded form x2+y2+Dx+Ey+F=0, which is what you get after multiplying out the brackets. The standard exam workflow is: if a circle is given in expanded form, complete the square in x and y to convert back to centre-radius form, then read off the centre and radius.
A short worked example. The equation x2+y2−6x+4y−12=0 does not immediately tell you anything geometric. Complete the square: x2−6x=(x−3)2−9 and y2+4y=(y+2)2−4. Substituting back gives (x−3)2−9+(y+2)2−4−12=0, which simplifies to (x−3)2+(y+2)2=25. The circle has centre (3,−2) and radius 5.
Many candidates lose marks through arithmetic slips when completing the square — forgetting to subtract the squared half-coefficient or making sign errors on the constant. A more conceptual pitfall is failing to check that the right-hand side is positive: if the completed-square form gives r2<0, there is no real circle. AQA sometimes embeds this as a check inside a longer question.
For practice on completing the square in two variables and a clean workflow for any circle equation, see the Equation of a Circle lesson.
Circle Properties
Once you can read off the centre and radius, the circle theorems from GCSE come back into force, now expressed algebraically. AQA expects you to be fluent with three results in particular.
The first is that a tangent to a circle is perpendicular to the radius at the point of contact. So if the centre is C and the point of contact is P, the tangent has gradient perpendicular to the gradient of CP. This single observation handles almost every tangent question.
The second is that the perpendicular from the centre to a chord bisects the chord. So to find the length of a chord, drop a perpendicular from the centre, use Pythagoras with the radius as hypotenuse, and double the result. This is the standard route into chord-length problems.
The third is that the angle in a semicircle is a right angle (Thales' theorem). If three points A, B and C lie on a circle and AB is a diameter, the angle at C is 90°. This appears in proof-style questions where you are asked to show that three given points lie on a circle, or that a particular angle is right.
A short worked example. Find the equation of the tangent to the circle (x−3)2+(y−2)2=25 at the point P(6,6). First check that P lies on the circle: 9+16=25, yes. The centre is C(3,2), so the gradient of CP is (6−2)/(6−3)=4/3. The tangent gradient is therefore −3/4. The tangent equation is y−6=−43(x−6), or 3x+4y=42.
A common pitfall is forgetting to check that the point actually lies on the circle. Another is mishandling perpendicular gradients when the radius is horizontal or vertical — the tangent is then vertical or horizontal, and −1/m does not apply directly.
For chord and tangent practice with worked diagrams, see the Circle Properties lesson.
Parametric Equations Introduction
A parametric equation describes a curve by writing both x and y as functions of a third variable, called the parameter, conventionally t. So instead of y=f(x), you have x=f(t) and y=g(t). As t varies, the point (x(t),y(t)) traces out a curve. This is the natural language for many curves — circles, ellipses, projectile paths, cycloids — that cannot be written cleanly as a single y=f(x).
The standard technique on AQA is converting between parametric and Cartesian form. To eliminate the parameter, solve one of the parametric equations for t and substitute into the other. Sometimes this is direct, as when x=t+1 and y=t2 give y=(x−1)2. Sometimes you need a trig identity. If x=3cost and y=3sint, square and add to get x2+y2=9, the equation of a circle of radius 3. Recognising that cos2t+sin2t=1 converts the parametric form instantly.
The parameter sometimes carries a restriction — for instance, 0≤t≤π — and that restriction translates into a restriction on the Cartesian curve. If x=3cost for 0≤t≤π, then x ranges over [−3,3] but y=3sint is non-negative throughout, so the parametric curve is only the upper half of the circle. AQA likes to test this — write the Cartesian equation including any restriction on x or y.
A common pitfall is dropping the restriction when you eliminate t. The Cartesian equation by itself describes a longer curve than the parametric equations actually trace out. Another is mis-applying the trig identity, particularly when the parametric coefficients differ — for x=2cost and y=3sint, the right manipulation is (x/2)2+(y/3)2=1, an ellipse.
For parametric-to-Cartesian conversion practice, see the Parametric Equations Introduction lesson.
Parametric Differentiation
To find the gradient of a parametric curve, AQA uses the chain rule:
dxdy=dx/dtdy/dt.
So you differentiate y with respect to t, differentiate x with respect to t, and divide. The result is in general a function of t, not of x. To find the gradient at a particular point, substitute the value of t that corresponds to that point.
A short worked example. A curve has parametric equations x=t2+1 and y=t3−3t. Then dx/dt=2t and dy/dt=3t2−3, so dy/dx=(3t2−3)/(2t)=3(t2−1)/(2t). To find the tangent at the point where t=2, substitute: dy/dx=3(3)/4=9/4. The point is (5,2), so the tangent is y−2=49(x−5).
For a horizontal tangent, set dy/dt=0 and solve for t. For a vertical tangent, set dx/dt=0 and solve. Be careful about points where both vanish simultaneously — these are singular points and the gradient is genuinely undefined there, not zero. AQA occasionally examines this distinction inside a stationary-point question on a parametric curve.
A common pitfall is forgetting to include the substitution back to find the actual point on the curve once you have t. Another is computing dy/dx as dy/dt divided into dx/dt instead of the other way round — the right form is "top over bottom in t", dy/dt over dx/dt.
For full coverage with tangent and normal problems, see the Parametric Differentiation lesson.
Parametric Integration
To find the area under a parametric curve, AQA uses the substitution rule applied to ∫ydx. Replace dx by (dx/dt)dt and replace the limits in x by the corresponding limits in t. The integral becomes
Area=∫t1t2y(t)⋅dtdxdt,
where t1 and t2 are the parameter values at the endpoints of the region.
A short worked example. A curve has parametric equations x=t2 and y=2t+1 for 0≤t≤2. The area between the curve, the x-axis and the lines x=0 and x=4 is
∫02(2t+1)⋅2tdt=∫02(4t2+2t)dt=[34t3+t2]02=332+4=344.
A common pitfall is forgetting to convert the limits when you switch from x to t. If the original integral runs from x=0 to x=4 and the parameter runs from t=0 to t=2, you must integrate from 0 to 2, not 0 to 4. Another is dropping the dx/dt factor — without it, you are not computing an area at all, just an integral of y with respect to t, which is a different quantity.
A second style of question asks for an area where part of the curve dips below the x-axis. AQA generally wants the signed integral unless the question explicitly asks for the geometric (always-positive) area. Read the question, not the formula.
For worked examples on areas under parametric curves, see the Parametric Integration lesson.
Implicit Differentiation
An implicit equation is one where x and y are tangled together so that you cannot easily solve for y — for example, x2+xy+y3=7. To find dy/dx, you differentiate both sides of the equation with respect to x, treating y as a function of x throughout. Every time you differentiate a term containing y, the chain rule produces a factor of dy/dx.
A short worked example. Differentiate x2+xy+y3=7 implicitly. The left side gives 2x+(y+x⋅dy/dx)+3y2⋅dy/dx, using the product rule on xy and the chain rule on y3. The right side is zero. Collecting terms in dy/dx:
2x+y+(x+3y2)dxdy=0,
so dy/dx=−(2x+y)/(x+3y2). The gradient at any point (x,y) on the curve is read off by substitution.
The most useful application is finding tangents and normals to a curve where y cannot be isolated. The implicit derivative gives the gradient at a known point; the tangent and normal then follow from the standard point-gradient form. Implicit differentiation is also the right tool for related-rates problems, where two variables both depend on time and an equation links them.
A common pitfall is forgetting the chain-rule factor of dy/dx on y-terms. Another is mis-applying the product rule on xy — it is y+x⋅dy/dx, not x⋅dy/dx alone. A third is failing to substitute the point coordinates correctly into the implicit derivative; you need both x and y values.
For full practice with tangent, normal and stationary-point problems on implicit curves, see the Implicit Differentiation lesson.
Curve Sketching Strategies
Curve sketching is a transferable skill that AQA tests across the whole specification. The aim is not a perfectly proportioned drawing — it is a sketch that captures the key features clearly. There is a reliable workflow that handles almost any curve given to you in the exam.
| Step | What to find | Why it matters |
|---|---|---|
| Intercepts | Set y=0 for x-intercepts, x=0 for y-intercept | Fixes where the curve meets the axes |
| Stationary points | Set dy/dx=0 and solve | Locates maxima, minima, points of inflection |
| Asymptotes | Vertical: where denominator vanishes. Horizontal: limit as x→±∞ | Constrains the long-distance behaviour |
| End behaviour | Sign of leading term as x→±∞ | Tells you which way the curve goes off the page |
| Symmetries | Even, odd, periodic, point-symmetric | Halves your work if present |
For polynomials, the workflow is short: factorise, mark the roots with their multiplicities (simple roots cross the axis, double roots touch and turn), and use the leading coefficient to fix the end behaviour. For rational functions, the asymptotes do most of the work — once you have them, the curve threads through in the obvious way. For trig curves, the period and amplitude pin the shape; sketch one period and then translate.
A common pitfall is sketching to scale rather than to shape. AQA mark schemes award method marks for correct intercepts, correct asymptotes, correct end behaviour and correct turning behaviour at multiple roots. They do not award marks for accurate proportions. Another pitfall is missing a vertical asymptote — always check for values of x that make a denominator zero.
For a full sketching workflow with worked examples on polynomials, rationals and parametric curves, see the Curve Sketching Strategies lesson.
Intersection Problems
An intersection problem asks you to find where two curves meet. The general method is simultaneous equations: solve the two curve equations together. The kind of equation you end up with depends on the curves. Two straight lines give a single linear equation. A line and a circle give a quadratic. Two circles give a linear equation (after subtracting one circle from the other) plus one of the circles. A parametric curve and a Cartesian curve usually require eliminating the parameter first.
The discriminant has a powerful geometric meaning at intersections. If a line meets a curve and the resulting quadratic has discriminant b2−4ac>0, the line cuts the curve at two distinct points. If the discriminant is zero, the line is tangent to the curve (one repeated intersection). If the discriminant is negative, the line and the curve do not meet. Tangency conditions are a classic AQA question — you are given a line with a parameter k and asked to find the value of k for which the line is tangent to the circle or curve.
A short worked example. For what values of k is the line y=kx+1 tangent to the circle x2+y2=4? Substitute: x2+(kx+1)2=4, expand to (1+k2)x2+2kx−3=0. For tangency, the discriminant is zero: (2k)2−4(1+k2)(−3)=0, so 4k2+12+12k2=0, which gives 16k2=−12. There is no real k — meaning no line of the given form through (0,1) is tangent. The point (0,1) lies inside the circle, so any line through it must cross the circle in two points. The algebra confirms the geometry.
A common pitfall is solving for x and forgetting the corresponding y values. Another is making sign or expansion errors on a long substitution. Rushing the algebra here costs more marks than rushing anywhere else.
For tangency, two-circle and parametric-Cartesian intersection problems, see the Intersection Problems lesson.
Loci and Geometric Proof
A locus is the set of all points that satisfy a given geometric condition. The classic loci on AQA are: the locus of points equidistant from two given points (the perpendicular bisector of the segment between them); the locus of points at a fixed distance from a given point (a circle); and the locus of points equidistant from a point and a line (a parabola, though AQA only asks for the equation, not the curve sketch). Less common but examined are loci defined by ratio of distances or by a sum of distances.
The standard technique is to translate the geometric condition into an algebraic equation in x and y. If the locus is the set of points equidistant from A(1,2) and B(5,8), the condition is
(x−1)2+(y−2)2=(x−5)2+(y−8)2.
Square both sides, expand, and simplify. The squared roots cancel and you are left with a linear equation: −2x−4y+5=−10x−16y+89, which simplifies to 8x+12y=84, or 2x+3y=21. This is the perpendicular bisector you would have got from the straight-line method earlier — confirmation that the locus interpretation matches the geometry.
Loci questions often blend with geometric proof. AQA expects you to be able to prove statements like "the locus of points equidistant from A and B is the perpendicular bisector of AB" by direct algebra, or to prove that three given points are collinear, or that a particular triangle is right-angled. The proof structure is: state what you are proving, set up coordinates or vectors, derive the algebraic condition, and conclude with a clear "therefore". A proof that ends without an explicit conclusion loses the final mark.
A common pitfall is squaring the distance equation but failing to simplify carefully. Another is missing degenerate cases (a single point, or empty) where the geometric condition is too restrictive. Always sanity-check the final equation against the geometry.
For locus and proof practice with worked solutions, see the Loci and Geometric Proof lesson.
Common Mark-Loss Patterns Across Coordinate Geometry
Across the whole coordinate-geometry section, a small set of habits accounts for a disproportionate share of lost marks — content you do know, applied carelessly.
- Sign errors when completing the square on a circle equation. Half the coefficient, square it, subtract — and check at the end.
- Confusing parallel and perpendicular gradient rules under exam pressure. Parallel means equal; perpendicular means product is −1.
- Forgetting that a tangent is perpendicular to the radius at the point of contact. This single fact unlocks most tangent questions on circles.
- Dropping the parameter restriction when converting parametric to Cartesian form. The Cartesian equation alone may describe a longer curve than the original parametric pair traces out.
- Differentiating dy/dx as dx/dt over dy/dt instead of the other way round on parametric curves. The right form is (dy/dt)/(dx/dt).
- Forgetting the chain-rule factor of dy/dx on y-terms when differentiating implicitly.
- Mis-applying the product rule on a term like xy in implicit differentiation: d/dx(xy)=y+x⋅dy/dx.
- Missing a vertical asymptote when sketching a rational function. Always check denominators for zeros.
- Solving for x and forgetting to find the corresponding y in intersection problems. The question almost always asks for points.
- Ending a proof without an explicit conclusion. AQA mark schemes reserve the final mark for a clear "therefore" statement.
- Sketching to scale rather than to shape. Examiners want intercepts, asymptotes, end behaviour and turning points — not a perfectly proportioned graph.
A revision plan that explicitly drills these habits — not just the content — will move your grade more than another pass through the textbook.
Recommended Six-Week Revision Plan
This plan is designed for a candidate who has covered the coordinate-geometry content in lessons but wants to revise it cleanly before the exam. It assumes about 5-6 hours per week on this section. Adjust pace if you are starting earlier or later.
| Week | Topics | Practice |
|---|---|---|
| 1 | Straight lines review; equation of a circle | 20 straight-line problems including 5 perpendicular-bisector; 15 circle-equation problems involving completing the square |
| 2 | Circle properties (tangents, chords, perpendicular bisectors) | 10 tangent-to-circle problems; 10 chord-length problems; 5 mixed circle-property questions |
| 3 | Parametric equations introduction; parametric differentiation | 15 parametric-to-Cartesian conversions; 15 parametric-tangent problems |
| 4 | Parametric integration; implicit differentiation | 10 areas under parametric curves; 15 implicit differentiation problems including 5 tangent-and-normal |
| 5 | Curve sketching strategies; intersection problems; loci | 10 sketching problems across function types; 10 intersection problems including 5 tangency; 5 locus and proof problems |
| 6 | Mixed practice; targeted review of weakest topics; full coordinate-geometry question sets | One full mixed problem set per day; review marking-scheme working for any question scoring below 60% |
The point of the plan is to keep moving forward while maintaining contact with earlier topics. Do not spend three weeks on circles and run out of time before parametric integration. By the end of week 5, every topic should have had focused contact and a practice round. Week 6 is consolidation.
A useful discipline through the plan is to treat any wrong question as a diagnostic. Content gap? Method error? Arithmetic slip? Logging the cause means your next review targets the right thing.
How LearningBro's AQA A-Level Maths Coordinate Geometry Course Helps
LearningBro's AQA A-Level Maths: Coordinate Geometry course is built around the structure of this guide. Each of the ten lessons covers one section of the 7357 specification, in the order AQA tends to teach it, with worked examples, practice questions and full mark-scheme-style solutions. Lessons end with a short review and quick-recall questions designed for spaced revisits.
The course is designed to be used in two ways. As a first pass, you can work through the lessons in order, building each topic on the last. As a revision tool, you can drop into any lesson and work the practice independently — for example, drilling implicit differentiation for a week before mocks. The AI tutor is available throughout to give targeted hints when you get stuck, without giving away full solutions.
If you want one place to revise this section of the spec well, with realistic practice and clean explanations, the full course is the right next step. Start with the AQA A-Level Maths: Coordinate Geometry course.