The diagram shows a circle, centre , with diameter . The points and lie on the circle. The point is such that and are tangents to the circle.

- (a)
Given that the points and are midpoints of and respectively, prove that angle .
- (b)
Given that triangle is equilateral, prove that .
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Worked solution
3(a)
1. Identify the angle between the diameter and the tangent.
Since is a diameter and is a tangent to the circle at ,
(tangent radius).
2. Apply the Midpoint Theorem to triangle ABE.
In , is the midpoint of and is the midpoint of .
By the Midpoint Theorem, .
3. Use parallel lines to find angle DCE.
Since and is a transversal,
(corresponding angles).
Therefore, .
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3(b)
1. Identify the angles in the equilateral triangle
Since triangle is equilateral, .
2. Apply the alternate segment theorem to relate the angles
Since is a tangent to the circle at and is a chord, by the alternate segment theorem, the angle between the tangent and the chord is equal to the angle in the alternate segment.
Therefore, .
Since , it follows that .
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