What is the radius of the circle? 
Please help with this grade nine math problem.  How does one calculate the radius if the two sides of the right angle triangle are 85cm.  The sides of the triangle are tangent to the circle.

Let $a\ (=85{\rm cm})$ be the length of the legs and $r$ the radius of the circle. Then
$${1\over2}\bigl(\sqrt{2}a\bigr)+r=a\ ,$$
which implies
$$r=\left(1-{\sqrt{2}\over2}\right)\>a\ .$$
