In the diagram, O is the centre of the circle. DOEFG and AEB are straight lines and GA is a tangent to the circle at A. Angle AGD = 32° and angle BCD = 106°.

- (a)
angle GOA ,
Answer ...°
- (b)
angle BCF ,
Answer ...°
- (c)
angle BDA ,
Answer ...°
- (d)
angle DEA .
Answer ...°
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Worked solution
7(a)
1. Identify the right angle between the tangent and radius
Since is a tangent at and is a radius,
2. Use the angle sum of triangle $AOG$ to find $\angle GOA$
Since are collinear, .
In ,
7(b)
1. Identify the right angle subtended by diameter $DF$ at $C$
Since are collinear and is the centre, is a diameter of the circle.
Hence,
(angle in a semicircle).
2. Subtract to find $\angle BCF$
Given
and lies inside .
Therefore,
7(c)
1. Find the angle between chord $AD$ and radius $AO$
From part (a), .
Since are collinear,
In , as radii, so
2. Use the cyclic quadrilateral and tangent-chord theorem to find $\angle BDA$
Since lie on the circle, opposite angles of cyclic quadrilateral are supplementary:
Hence
Since is tangent at , , so the angle between tangent and chord is
By the tangent-chord theorem,
7(d)
1. Find $\angle DAE$ using the cyclic quadrilateral
Since are collinear, .
In cyclic quadrilateral ,
2. Find $\angle ADE$ using the radius triangle $AOD$
From part (a), .
Since are collinear,
As , triangle is isosceles, so
Since are collinear,
3. Use the angle sum of triangle $ADE$ to find $\angle DEA$
In triangle ,
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