Shape and Space 2
4 marks · NormalIn the circle below, centre O, angle BAC = 70° and chord BC is a diameter.
(a)[2 marks]
Calculate angle ABC.
(b)[2 marks]
Give a reason for your answer.
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Show answer
(a) 90 degrees
(b) Angle in a semicircle is always 90°.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Identifies use of the 'angle in a semicircle' theorem or uses triangle sum formula.
A1 (a) · 1 mark · Gives angle ABC = 90°.
B1 (b) · 2 marks · States the angle in a semicircle theorem as reason, or that angle at circumference subtended by diameter is 90°.
Worked solution
ABC is subtended by the diameter, so angle ABC = 90° (angle in a semicircle).