# What is the perimeter of a triangle, who has a circle inscribed in it with a radius of 4.2?

If you want a numeric answer , I'm sorry you can't have one. There could be simply so many triangles with radius of incircle as $4.2 c m$.
$r \cdot \frac{p}{2} = \triangle$ (where r is radius and p is perimeter and $\triangle$ is area of triangle)