Question 907020
This triangle is half of a square shaped region (intuition from Geometry knowledge).  The whole square region (if included both halves of the square) is {{{2*(12.5)=25}}} square meters.  Also, the diameter of the semicircle is 2r, if r is the radius.  The height of the triangle is r.  


{{{(1/2)(2r)*r=12.5}}}, using formula for area of a triangle. The triangle is isosceles, 45-45-90 type.


{{{2r^2=25}}}
{{{r^2=12.5}}}
{{{highlight(r=sqrt(12.5))}}}