The task is:
An optional triangles area should be $t$ and its circumscribed circle radius $=~R$ and its inscribed circles radius $=~r$. Prove that $\frac{t}{3} < Rr$.
I was trying to solve it by calculating the are of the triangle in a different way with heron's formula, but it didn't seem to be a good way to go.
Can you help me solving this problem by telling me the answer an a good desciption, so next time I could solve these kind of problems on my own?