Question

A circle has centre C and radius 4 cm.

The diagram shows the circle with a point
D which lies on the circle. The tangent at D
passes through the point E. EC = √65 cm.
Find
a) the size in radians of angle DCE
b) the area of the shaded region

Answer 1

Explanation:

EC = 165 cm (Given) Tangent of circle also makes 90°.

a) sind = Perpendicular Hypotenuse = CD = EC 165 => 0 = Sin = 0.519 ~ 0.52 =29.7448 ~ 29.75° =<E

By angle sum property of triangle. <D+<E+ <C = 180°

90° + 29.75 + LC = 180°

<C = 180-90-29.75 = 60.25° <C= 60.25°

<DCE = <C = 60.25 x π/180 = 1.052 radians.

(b) Area of triangle DCE = 1/2 x b x h = 1/2 x ED X 4

ED² + CD² = EC² ED² + 4² = (√65)² => EC² = 65-16 = 49 ED=7

Area = 1/2 x 7 x 4 = 14 cm²

Area of sector a π x 4²x 60.25/360 = 8.4125 cm2

Area of shaded region= Area ADCE Area of sector -

= 14-8.4125 = 5.5875 cm²

(a) <DCE = 1.052 radians b) Area shaded of region = 5.5875cm²