# Trigonometry 1

Geometry Level 5

In a triangle $$ABC$$ , $$\cos { A } .\cos { B } +\sin { A } .\sin { B } .\sin ^{ 2 }{ C } =1$$ and $$a$$, $$b$$, $$c$$ are lengths of sides . Find the value of $$\frac { r }{ R }$$