A green quadrilateral of which two sides are tangent to a quarter circle of radius r. What is its area?

Solution

The green area is r²/√2.

Poem

Walking in forest wild
Among the trees,
The lakes so bright
Green trees, oaks and pines
A green spot so nice I like
Far away from all pollution
This forest is a good solution
A good moment to share
With beloved people for whom
I care
To enjoy the scent and the sunlight

Bella