Question

A triangle is placed in a semicircle with a radius of 9 cm

Answer 1

Considering that the shaded area is the part of the semi circle outside the triangle:
Area of circle= Pi x radius2 (this means radius squared)
Area of triangle= 1/2 x base x height
1/2 (because it is a semi circle) x 3.14 (in replacement of pi as directed by question) x 9squared= 127.17

127.17 - (1/2 x 18 x 9) = 46.17cmsquared