Find the percentage of the area of a circle that is contained in an inscribed isosceles triangle, one of whose sides is the diameter of the circle

The diameter will be the longest side of the triangle......If we let this = 2r, the height of the triangle is r

So.... the area of the triangle is

(1/2)(2r) (r) = r^2

And the area of the circle is pi * r^2

So.....the ratio of the area is

r^2 / [ pi * r^2 ] =

1 / pi ≈ 31.8%