
Higher Maths
The Circle
Course content
- Determining and using both forms of the equation of a circle
- Using properties of tangents to circles
- Intersection of two circles
- Intersection of a line and a circle.
Textbook page references
- Zeta Higher Mathematics
pp.44-63
- Heinemann Higher Maths pp.210-228
- TeeJay Higher Maths pp.76-84
Given formulae
- \(x^2+y^2+2gx+2fy+c=0\) represents a circle centre \((-g,-f)\) and radius \(\sqrt{g^2+f^2-c}\)
- \((x-a)^2+(y-b)^2=r^2\) represents a circle centre \((a,b)\) and radius \(r\)
Find a Higher Maths tutor

Do you need a tutor for Higher Maths?
Click here to find a tutor in your area.
Example 1 (non-calculator)
A is the point \((-3,8)\).
B is the point \((1,-2)\).
AB is the diameter of a circle.
Find the equation of this circle.
Example 2 (non-calculator)
Circle \(C_1\) has equation \(x^2+y^2+4x-6y-12=0.\)
Circle \(C_2\) has centre \((1,-4).\)
The two circles have equal radii.
Find the equation of circle \(C_2.\)
Example 3 (non-calculator)
Circle \(C_1\) has equation \((x-1)^2+(y+7)^2=16.\)
Circle \(C_2\) has equation \(x^2+y^2-12x-10y+12=0.\)
(a) Write down the centres and radii of \(C_1\) and \(C_2\).
(b) Show that \(C_1\) and \(C_2\) do not intersect.
Recommended textbook
Zeta Maths: Higher Mathematics

Example 4 (non-calculator)
The point P\((6,-4)\) lies on the circle \(x^2+y^2-4x+2y-20=0.\)
Find the equation of the tangent to the circle at P.
Example 5 (non-calculator)
Show that the line with equation \(y=2x-3\) is a tangent to the circle with equation \(x^2+y^2-8x+11=0\) and find the coordinates of the point of contact.
Example 6 (non-calculator)
The circle with equation \(x^2+y^2-6x-14y+k=0\) meets the coordinate axes at exactly three points, none of which are the origin. What is the value of \(k\)?
Revision guides
How to Pass Higher Maths
BrightRED Higher Maths Study Guide

Example 7 (non-calculator)
Given that the equation \(x^2+y^2-2px-4py+3p+2=0\) represents a circle, determine the range of values of \(p.\)
Example 8 (non-calculator)
SQA Higher Maths 2016 Paper 1 Q8
Show that the line with equation \(y=3x-5\) is a tangent to the circle with equation \(x^2+y^2+2x-4y-5=0\) and find the coordinates of the point of contact.
Example 9 (non-calculator)
SQA Higher Maths 2017 Paper 1 Q2
The point P\((-2,1)\) lies on the circle \(x^2+y^2-8x-6y-15=0.\)
Find the equation of the tangent to the circle at P.
Practice papers
Essential Higher Maths Exam Practice
Higher Practice Papers: Non-Calculator

Higher Practice Papers: Calculator

Example 10 (non-calculator)
SQA Higher Maths 2019 Paper 1 Q3
Circle \(C_1\) has equation \(x^2+y^2-6x-2y-26=0.\)
Circle \(C_2\) has centre \((4,-2).\)
The radius of \(C_2\) is equal to the radius of \(C_1\small.\)
Find the equation of circle \(C_2.\)
Example 11 (non-calculator)
SQA Higher Maths 2024 Paper 1 Q7
The line \(y=2x\) is a tangent to the circle with equation \(x^2+y^2-14x-8y+45=0\small.\) Determine the coordinates of the point of contact.
Need a Higher Maths tutor?
Just use this handy little widget and our partner Bark.com will help you find one.
Past paper questions
Finding equation of circle: • Specimen Paper 1 Q2 • Specimen Paper 2 Q12 • 2016 Paper 1 Q4 • 2017 Paper 2 Q10(b) • 2018 Paper 2 Q5 (with straight line) • 2018 Paper 2 Q12 (with collinearity) • 2019 Paper 1 Q3 • 2019 Paper 2 Q15(b) • 2021 Paper 1 Q15 • 2022 Paper 2 Q9(b) |
Tangent to a circle: • 2015 Paper 1 Q11 • 2016 Paper 1 Q8 • 2017 Paper 1 Q2 • 2018 Paper 1 Q4 • 2019 Paper 2 Q15(a) • 2021 Paper 2 Q14 |
Intersection of lines and circles: • Specimen Paper 1 Q7 • 2016 Paper 1 Q8 • 2017 Paper 2 Q3 • 2021 Paper 2 Q15 • 2022 Paper 2 Q9a • 2023 Paper 2 Q15 |
Intersection of two circles: • Specimen Paper 2 Q12 • 2015 Paper 2 Q5 • 2016 Paper 2 Q4 • 2018 Paper 2 Q12 • 2022 Paper 1 Q14 • 2023 Paper 2 Q11 |
Other question types: • 2015 Paper 1 Q14 • 2019 Paper 1 Q16 (with inequations) |
Other great resources
Detailed notes - HSN |
Detailed notes - Rothesay Academy |
Revision notes - BBC Bitesize |
Notes - Airdrie Academy |
Notes and examples - Maths Mutt |
Key points - Perth Academy |
Notes and videos - Mistercorzi 1. The circle equation 2. Lines and circles 3. Problem solving with circles |
Lesson notes - Maths 777 1. Equations of circles 2. Circles and lines 3. Intersection of circles |
Videos - Larbert High School 1. Equations of circles 2. General equation 3. Equations of tangents 4. Lines intersecting circles 5. Intersecting circles |
Videos - Maths180.com |
Videos - Mr Thomas Maths |
Videos - Siōbhán McKenna |
Worksheets - Brannock High School 1. Tangent to a circle (Answers) 2. Lines and circles (Answers) |
⇦ Higher topic list ⇧ Top of this page
|