a semicircle has a radius of 10 . 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 * 10 + 2 * 10 which is about 51 . the answer is e ."
add(divide(circumface(10), const_2), multiply(const_2, 10))