Circle equation from centre and radius

Given the centre coordinates and radius (or a point on the circle), find the equation of the circle in standard or expanded form.

11 questions · Easy -1.2

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Edexcel C2 2012 January Q2
4 marks Easy -1.8
2. A circle \(C\) has centre \(( - 1,7 )\) and passes through the point \(( 0,0 )\). Find an equation for \(C\).
(4)
Edexcel C2 Specimen Q2
4 marks Easy -1.2
The circle \(C\) has centre \(( 3,4 )\) and passes through the point \(( 8 , - 8 )\). Find an equation for C
OCR C1 2008 January Q2
3 marks Easy -1.3
2
  1. Write down the equation of the circle with centre \(( 0,0 )\) and radius 7 .
  2. A circle with centre \(( 3,5 )\) has equation \(x ^ { 2 } + y ^ { 2 } - 6 x - 10 y - 30 = 0\). Find the radius of the circle.
OCR MEI C1 Q5
12 marks Moderate -0.5
5
  1. Find the equation of the line passing through \(\mathrm { A } ( - 1,1 )\) and \(\mathrm { B } ( 3,9 )\).
  2. Show that the equation of the perpendicular bisector of AB is \(2 y + x = 11\).
  3. A circle has centre \(( 5,3 )\), so that its equation is \(( x - 5 ) ^ { 2 } + ( y - 3 ) ^ { 2 } = k\). Given that the circle passes through A , show that \(k = 40\). Show that the circle also passes through B .
  4. Find the \(x\)-coordinates of the points where this circle crosses the \(x\)-axis. Give your answers in surd form.
OCR MEI C1 Q7
12 marks Moderate -0.8
7
  1. Find the equation of the line passing through \(\mathrm { A } ( - 1,1 )\) and \(\mathrm { B } ( 3,9 )\).
  2. Show that the equation of the perpendicular bisector of AB is \(2 y + x = 11\).
  3. A circle has centre \(( 5,3 )\), so that its equation is \(( x - 5 ) ^ { 2 } + ( y - 3 ) ^ { 2 } = k\). Given that the circle passes through A , show that \(k = 40\). Show that the circle also passes through B .
  4. Find the \(x\)-coordinates of the points where this circle crosses the \(x\)-axis. Give your answers in surd form.
OCR PURE 2023 May Q6
10 marks Moderate -0.3
6 The vertices of triangle \(A B C\) are \(A ( - 3,1 ) , B ( 5,0 )\) and \(C ( 9,7 )\).
  1. Show that \(A B = B C\).
  2. Show that angle \(A B C\) is not a right angle.
  3. Find the coordinates of the midpoint of \(A C\).
  4. Determine the equation of the line of symmetry of the triangle, giving your answer in the form \(p x + q y = r\), where \(p , q\) and \(r\) are integers to be determined.
  5. Write down an equation of the circle with centre \(A\) which passes through \(B\). This circle intersects the line of symmetry of the triangle at \(B\) and at a second point.
  6. Find the coordinates of this second point.
OCR MEI Paper 2 2021 November Q7
4 marks Easy -1.2
7 The parametric equations of a circle are
\(x = 7 + 5 \cos \theta , \quad y = 5 \sin \theta - 3\), for \(0 \leqslant \theta \leqslant 2 \pi\).
  1. Find a cartesian equation of the circle.
  2. State the coordinates of the centre of the circle. Answer all the questions.
    Section B (77 marks)
OCR Mechanics 1 2018 December Q3
5 marks Moderate -0.8
3
\includegraphics[max width=\textwidth, alt={}, center]{918c616a-a0c7-4779-8d3c-84ddf1fa36d6-04_695_714_1087_248} The diagram shows a circle with centre \(( a , - a )\) that passes through the origin.
  1. Write down an equation for the circle in terms of \(a\).
  2. Given that the point \(( 1 , - 5 )\) lies on the circle, find the exact area of the circle.
AQA Paper 1 2022 June Q13
9 marks Moderate -0.8
13 Figure 2 shows the approximate shape of the vertical cross section of the entrance to a cave. The cave has a horizontal floor. The entrance to the cave joins the floor at the points \(O\) and \(P\). \begin{figure}[h]
\captionsetup{labelformat=empty} \caption{Figure 2} \includegraphics[alt={},max width=\textwidth]{22ff390e-1360-43bd-8c7f-3d2b58627e91-24_396_991_584_529}
\end{figure} Garry models the shape of the cross section of the entrance to the cave using the equation $$x ^ { 2 } + y ^ { 2 } = a \sqrt { x } - y$$ where \(a\) is a constant, and \(x\) and \(y\) are the horizontal and vertical distances respectively, in metres, measured from \(O\). 13
  1. The distance \(O P\) is 16 metres.
    Find the value of \(a\) that Garry should use in the model.
    \includegraphics[max width=\textwidth, alt={}, center]{22ff390e-1360-43bd-8c7f-3d2b58627e91-25_2518_1723_196_148}
AQA Paper 2 2022 June Q1
1 marks Easy -2.5
1 A circle has centre \(( 4 , - 5 )\) and radius 6
Find the equation of the circle.
Tick ( \(\checkmark\) ) one box. $$\begin{aligned} & ( x - 4 ) ^ { 2 } + ( y + 5 ) ^ { 2 } = 6 \\ & ( x + 4 ) ^ { 2 } + ( y - 5 ) ^ { 2 } = 6 \\ & ( x - 4 ) ^ { 2 } + ( y + 5 ) ^ { 2 } = 36 \\ & ( x + 4 ) ^ { 2 } + ( y - 5 ) ^ { 2 } = 36 \end{aligned}$$ □



AQA Paper 2 2024 June Q1
1 marks Easy -2.0
1 One of the equations below is the equation of a circle. Identify this equation. Tick ( ✓ ) one box.
\(( x + 1 ) ^ { 2 } - ( y + 2 ) ^ { 2 } = - 36\) □
\(( x + 1 ) ^ { 2 } - ( y + 2 ) ^ { 2 } = 36\) □
\(( x + 1 ) ^ { 2 } + ( y + 2 ) ^ { 2 } = - 36\) □
\(( x + 1 ) ^ { 2 } + ( y + 2 ) ^ { 2 } = 36\) □