a semicircle has a radius of 9 . what is the approximate perimeter of the semicircle ?
"the perimeter of a circle is 2 * pi * r . the perimeter of a semicircle is 2 * pi * r / 2 + 2 r = pi * r + 2 r the perimeter is pi * 9 + 2 * 9 which is about 46 . the answer is d ."
add(divide(circumface(9), const_2), multiply(const_2, 9))