Answer:

Step-by-step explanation:
<em>Look at the picture.</em>
We have the triangles 45° - 45° - 90°. The sides are in ratio 1 : 1 : √2
(<em>look at the second picture</em>).
Therefore we have the equations:
and 
Solve:
<em>multiply both sides by √2</em>
<em>divide both sides by 2</em>

<em>multiply both sides by √2</em>
<em>divide both sides by 2</em>

The side length of square is

The area of a square:
