5 semicircles are drawn as shown in figure. If AB : BC:CD= 3 : 2 : 6 then the ratio of area of
shaded region to that of unshaded region is 76 : 1, then I is :
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Answer:
Area of the shaded region = Area of circle with center at O - Area of semicircle with center at O-Area of smaller semicircle with radius r
′
-Area of smaller semicircle with radius r
′
Here, r=
2
28
=14
r
′
=
2
r
=>r
′
=
2
14
=>r
′
=7
Area of the shaded region =πr
2
−
2
πr
2
−
2
πr
′
2
−
2
πr
′
2
=
2
πr
2
−πr
′
2
=
2
π×14
2
−π7
2
=
2×7
22×14×14
−
7
22×7×7
=22×14−22×7
=22×7
=154cm
2
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