Find the colored area

Geometry Level 3

  • I I is the center of the circle.

  • I A = 8 IA = 8 cm

  • A I D = 13 5 \angle AID = 135^\circ

  • A B = B D = C D = H G = G F = F E AB=BD=CD=HG=GF=FE

What is the colored area to 3 decimal places?


The answer is 65.297.

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3 solutions

The shaded area is composed of 2 2 sectors of a circle and 6 6 segments of a circle. By some calculations the central angle of each is 4 5 45^\circ . Therefore the area of the shaded region is

2 ( 45 360 ) ( π ) ( 8 2 ) + 6 [ 45 360 ( π ) ( 8 2 ) 1 2 ( 8 2 ) ( sin 45 ) ] 2\left(\dfrac{45}{360}\right)(\pi)(8^2)+6\left[\dfrac{45}{360}(\pi)(8^2)-\dfrac{1}{2}(8^2)(\sin 45)\right]\approx 65.29743 \boxed{65.29743}

Yahia El Haw
Apr 19, 2016

Brian Chiang
Apr 19, 2016

8^2 π - 8^2sin(45)/2 * 6 = 65.2974...

You find the whole area of the circle, and subtract the 6 triangles using the law of sine: A = absin(C) which a and b are the sides and C is an angle in between. In this question the sides of the triangle are the radius. Using a calculater and these methods, you will be able to find and round the answer easily, which is 65.297 to the 3 decimal places.

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