Posted by Jason on Wednesday, March 27, 2013 at 11:52pm.
ABCD is a trapezoid with AB < CD and AB parallel to CD. \Gamma is a circle inscribed in ABCD, such that \Gamma is tangent to all four sides. If AD = BC = 25 and the area of ABCD is 600, what is the radius of \Gamma?

Geometry  Raffaele, Thursday, March 28, 2013 at 7:44am
in a trapezoid like this the sum of two opposite sides is equal to the sum of the other two
thus the sum of the bases is 50
area = (1/2)(sum of the bases) x height
height = (2 area)/(sum of the bases)
height = 1200/50 = 24
height is also the diameter of the circle
therefore its radius is 12