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1.5.5 Circular Measure, Long Questions (Question 9)


Question 9:
In diagram 5, AOBDE, is a semicircle with centre O and has radius of 5cm. ABC is a right angle triangle.


It is given that AD DC =3.85 and DC=2.31 cm.  
[Use π = 3.142]
Calculate
(a) the value of θ, in radians,   [2 marks]
(b) the perimeter, in cm, of the segment ADE,    [3 marks]
(c) the area, in cm2, of the shaded region BCDF.   [5 marks]


Solution:
(a)
Given  AD DC =3.85 and DC=2.31 cm AD=3.85×2.31=8.8935 AC=8.8935+2.31=11.2035 cm cosθ= AB AC = 10 11.2035 θ= 26.80 o θ= 26.80 o × π 180 o =0.4678 rad

(b)
∠AOD = 3.142 – (0.4678 × 2)
= 2.206 rad
Length of arc AED = 5 × 2.206
= 11.03 cm
Therefore, perimeter of the segment ADE
= 11.03 + 8.8935
= 19.924 cm

(c)
BC = √ AC2AB2
  = √11.20352 – 102
  = 5.052 cm

2.206 rad× 180 o π = 126.38 o BOD=3.1422.206=0.936 rad Area of shaded region BCDF =Area of  ABCArea of  AODArea of segment OBD = 1 2 ( 10 )( 5.052 ) 1 2 ( 5 )( 5 )( sin126.38 ) 1 2 ( 5 ) 2 ( 0.936 ) =25.2610.0611.7 =3.50  cm 2


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