What is the measure of the radius of the circle inscribed in a triangl

First, checking if the triangle is a right triangle by plugging in the numbers in Pythagorean Theorem: 8^2 + 15^2 = 17^2 -> It is.
Area of triangle therefor is 1/2 * 8 * 15 = 60.

Then realizing that for the circle to be inscribed in the triangle, it can not have an area greater than 60.

Checking the area of square using the answer choices and area of square formula Pi*r^2:
(I squared the numbers first, then checked for Pi only if necessary.)

(A) 8.5: 8^2 is already 64, so OUT.
(B) 6: 6^2 = 36 and 36 * Pi, with Pi being roughly 3, is definitely greater than 60, so OUT.
(C) 3: 3^2 = 9 and 9 * Pi is smaller than 60, so KEEP.
(D) 5: 5^2 = 25 and 25 * Pi is greater than 60, so OUT.
(E) 12: 12^2 is way too big, we already ruled out 8.5, 6, and 5 so it also can't be 12, so OUT.

Leaves us only with (C).

Is this formula applicable only for right angle triangles? Thanks

Posted from my mobile device