Question 834211
Since the radius is 2.5, the diameter is 5.
A diagonal for the rectangle is equal to this diameter.
We have a triangle with side lengths of 5 and 4.
5 is the hypotenuse. Set x = the length of the 
other side of the triangle.
So {{{4^2 + x^2 = 5^2}}}
{{{16 + x^2 = 25}}}
add -16 to each side
{{{x^2 = 9}}}
x = 3
We have side lengths of 3 and 4 so
the area = 3*4 = 12