Geometry  semicircle inside isosceles triangle
posted by Knights .
Isosceles triangle ABC has sides of length AB=AC=25 and BC=40 . Find the area of a semicircle inscribed in triangle ABC with diameter along BC .
Please help I do not know how to start....

If the center of the semicircle is O, draw OD where D is the point where AC is tangent to o the circle.
Since OD┴AD, if the radius is r, let a=AD and b=DC, so a+b=25
r^2 + a^2 =15^2
r^2 + b^2 = 20^2
equating r^2, we get
15^2a^2 = 20^2(25a)^2
solve to get a=9, so b=16
So, r^2+9^2 = 15^2
r^2 = 22581=144
area of semicircle is 1/2 pi r^2 = 72pi 
Thanks a lot!

Stop Cheating!

Wow...AoPS caught you...don't know what to say...
However, it is still quite funny... 
In violation of our honor code. The previous AoPS was an imposter, his username had an uppercase "O" instead of the correct lowercase o.

i agree and please ask for hints on the message boards. THe questions are supposed to be challenging try to solve them by yourself