Discia GCSE Maths › Geometry & Measures › Circle Theorems

Circle Theorems worksheet

10 GCSE practice questions with answers, free to print. Every sheet is generated, so you can make a fresh one whenever you need it.

10 questions 29 marks Sheet 1
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  1. 2 marks

    \(A\), \(B\) and \(C\) are points on a circle, centre \(O\).

    A circle with centre O. A and B are on the circle and joined to O. C is on the circle on the far side of AB from O, and is joined to A and to B. The angle AOB at the centre is marked 130 degrees and the angle ACB at C is marked x.130°xABCO
    (a)

    Calculate the size of the angle marked \(x\).

    (b)

    Give a reason for your answer.

  2. 2 marks

    \(A\), \(B\), \(C\) and \(D\) are points on a circle.

    A circle with A, B, C and D on it. C and D are both on the same side of the chord AB, and each is joined to A and to B. The angle ACB is marked 35 degrees and the angle ADB is marked x.35°xABCD
    (a)

    Write down the size of the angle marked \(x\).

    (b)

    Explain your answer.

  3. 4 marks

    \(A\), \(B\) and \(C\) are points on a circle, centre \(O\).

    \(AB\) is a diameter of the circle.

    A circle with centre O. AB is a diameter and C is a point on the circle. C is joined to A and to B. The angle CAB is marked 59 degrees and the angle ABC is marked x.59°xABCO
    (a)

    State the size of angle \(ACB\).

    (b)

    Explain your answer.

    (c)

    Calculate the size of the angle marked \(x\).

  4. 4 marks

    \(A\), \(B\), \(C\) and \(D\) are points on a circle.

    A circle with A, B, C and D on it in order, joined up to make the quadrilateral ABCD. The angle at A is marked 78 degrees, the angle at B is marked 101 degrees and the angle at C is marked x.78°101°xABCD
    (a)

    Work out the size of the angle marked \(x\).

    (b)

    Give a reason for your answer.

    (c)

    Work out the size of angle \(ADC\).

  5. 4 marks

    \(A\) and \(B\) are points on a circle, centre \(O\).

    \(PA\) and \(PB\) are tangents to the circle.

    A circle with centre O. PA and PB are tangents to the circle, touching it at A and at B, and OA and OB are drawn. The angle APB is marked 60 degrees and the angle AOB at the centre is marked x.60°xABPO
    (a)

    Write down the size of angle \(OAP\).

    (b)

    Give a reason for your answer.

    (c)

    Calculate the size of the angle marked \(x\).

  6. 3 marks

    \(PA\) and \(PB\) are tangents to a circle, touching it at \(A\) and at \(B\).

    A circle with A and B on it. PA and PB are tangents to the circle, touching it at A and at B, and the chord AB is drawn. The angle APB is marked 68 degrees and the angle PAB is marked x.68°xABP
    (a)

    Find the size of the angle marked \(x\).

    (b)

    Give a reason why triangle \(ABP\) is isosceles.

  7. 2 marks

    \(T\), \(A\) and \(B\) are points on a circle.

    The straight line through \(T\) is a tangent to the circle.

    A circle with T, A and B on it. A straight line touches the circle at T, and T is joined to A and to B, with A joined to B as well. The angle between the tangent and the chord TA is marked x, and the angle TBA on the other side of TA is marked 49 degrees.x49°TAB
    (a)

    Write down the size of the angle marked \(x\).

    (b)

    Explain your answer.

  8. 2 marks

    \(A\), \(B\) and \(C\) are points on a circle, centre \(O\).

    A circle with centre O. A and B are on the circle and joined to O. C is on the circle on the far side of AB from O, and is joined to A and to B. The angle AOB at the centre is marked 46 degrees and the angle ACB at C is marked x.46°xABCO
    (a)

    Calculate the size of the angle marked \(x\).

    (b)

    Give a reason for your answer.

  9. 2 marks

    \(A\), \(B\), \(C\) and \(D\) are points on a circle.

    A circle with A, B, C and D on it. C and D are both on the same side of the chord AB, and each is joined to A and to B. The angle ACB is marked 65 degrees and the angle ADB is marked x.65°xABCD
    (a)

    Write down the size of the angle marked \(x\).

    (b)

    Explain your answer.

  10. 4 marks

    \(A\), \(B\) and \(C\) are points on a circle, centre \(O\).

    \(AB\) is a diameter of the circle.

    A circle with centre O. AB is a diameter and C is a point on the circle. C is joined to A and to B. The angle CAB is marked 23 degrees and the angle ABC is marked x.23°xABCO
    (a)

    Write down the size of angle \(ACB\).

    (b)

    Give a reason for your answer.

    (c)

    Find the size of the angle marked \(x\).

Answers

  1. (a) \(65^\circ\)
    (b) The angle at the centre is twice the angle at the circumference
  2. (a) \(35^\circ\)
    (b) Angles in the same segment are equal
  3. (a) \(90^\circ\)
    (b) The angle in a semicircle is 90 degrees
    (c) \(31^\circ\)
  4. (a) \(102^\circ\)
    (b) Opposite angles of a cyclic quadrilateral add up to 180 degrees
    (c) \(79^\circ\)
  5. (a) \(90^\circ\)
    (b) The angle between a tangent and a radius is 90 degrees
    (c) \(120^\circ\)
  6. (a) \(56^\circ\)
    (b) The two tangents drawn from a point to a circle are equal in length, so PA = PB
  7. (a) \(49^\circ\)
    (b) The angle between a tangent and a chord is equal to the angle in the alternate segment
  8. (a) \(23^\circ\)
    (b) The angle at the centre is twice the angle at the circumference
  9. (a) \(65^\circ\)
    (b) Angles in the same segment are equal
  10. (a) \(90^\circ\)
    (b) The angle in a semicircle is 90 degrees
    (c) \(67^\circ\)

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