The diameter of semicircle
with center at
is thrice the radius of semicircle
with center at
. Quadrilateral
is a rectangle and triangle
is an equilateral triangle. The altitude of triangle
is twice the radius of semicircle
. If the area of triangle
is
, find the area of the whole figure.
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A A B C = 2 1 b h
3 2 = 2 1 ( 2 r ) ( 2 r )
6 4 = 4 r 2
1 6 = 4 r
r = 4
It follows that the diameter of semicircle n is 3 ( 4 ) = 1 2 and C E = B D = 1 2 and D E = B C = 8 .
So the area of semicircle n is 2 1 π ( 4 2 ) = 8 π . The area of semicircle m is 2 1 π ( 6 2 ) = 1 8 π . The area of rectangle B C E D is 8 ( 1 2 ) = 9 6 . The area of equilateral triangle F B D is 4 3 ( 1 2 2 ) = 3 6 3 .
Finally, the area of the whole figure is
3 2 + 9 6 + 3 6 3 + 8 π + 1 8 π = 1 2 8 + 3 6 3 + 2 6 π
Formulas used:
A = π r 2 ⟹ Area of a circle where r is the radius. When looking for the area of a semicircle, we need to divide it by 2 .
A = 4 3 x 2 ⟹ Area of an equilateral triangle where x is the side length. It is a derived formula.
A = l w ⟹ Area of a rectangle where l is the length and w is the width. It can also be b a s e × h e i g h t or l e n g t h × b r e a d t h