Question

The figure shown below is composed of a semicircle and a non-overlapping equilateral triangle and contains a hole that is also composed of a semicircle and a non-overlapping equilateral triangle. if the radius of the larger semicircle is 8, and the radius of the smaller semicircle is ⅓, find the area of the figure.

Answer 1

Check the picture below.

since we know the radius of the larger semicircle is 8, thus its diameter is 16, which is the length of one side of the equilateral triangle. We also know the smaller semicircle has a radius of 1/3, and thus a diameter of 2/3, namely the lenght of one side of the small equilateral triangle.

now, if we just can get the area of the larger figure and the area of the smaller one and subtract the smaller from the larger, we'll be in effect making a hole/gap in the larger and what's leftover is the shaded figure.

`\bf \stackrel{\textit{area of a semi-circle}}{A=\cfrac{1}{2}\pi r^2\qquad r=radius}~\hspace{10em}\stackrel{\textit{area of an equilateral triangle}}{A=\cfrac{s^2√(3)}{4}\qquad s=\stackrel{side's}{length}} \\\\[-0.35em] ~\dotfill\\\\ \stackrel{\textit{\Large Areas}}{\left[ \stackrel{\textit{larger figure}}{\cfrac{1}{2}\pi 8^2~~+~~\cfrac{16^2√(3)}{4}} \right]\qquad -\qquad \left[ \cfrac{1}{2}\pi \left( \cfrac{1}{3} \right)^2 +\cfrac{\left( (2)/(3) \right)^2√(3)}{4}\right]}`

`\bf \left[ 32\pi +64√(3) \right]\qquad -\qquad \left[ \cfrac{\pi }{18}+\cfrac{(4)/(9)√(3)}{4} \right] \\\\\\ \left[ 32\pi +64√(3) \right]\qquad -\qquad \left[ \cfrac{\pi }{18}+\cfrac{√(3)}{9} \right]~~\approx~~ 211.38 - 0.37~~\approx~~ 211.01`