Circular Measure Long Questions (Question 3)

Question 3:

Diagram below shows a circle PQRT, centre Oand radius 5 cm. AQB is a tangent to the 
circle at Q. The straight lines, AO and BO, intersect the circle at P and R respectively. 
OPQR is a rhombus. ACB is an arc of a circle at centre O.

Calculate
(a) the angle x , in terms of p ,                                                                        
(b) the length , in cm , of the arc ACB ,                                                          
(c) the area, in cm2,of the shaded region.            

Solution:

(a)
Rhombus has 4 equal sides, therefore OP = PQ = QR = OR = 5 cm
OR is radius to the circle, therefore OR = OQ = 5 cm
Triangles OQR and OQP are equilateral triangle,
Therefore, Ð QOR= ÐQOP = 60o
Ð POR = 120o
x = 120o × p/180o

x = 2p/ 3 rad
(b) 
cos Ð AOQ= OQ / OA
cos 60o = 5 / OA
OA = 10 cm
Length of arc, ACB,
s = r θ
Arc ACB = (10) (2p / 3)
Arc ACB = 20.94 cm

(c)

Area of shaded region = 1 2 r 2 ( θ−sinθ ) ( change calculator to Rad mode ) = 1 2 ( 10 ) 2 ( 2π 3 −sin 2π 3 ) =50( 2.094−0.866 ) =61.40  cm 2

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