Square moves in a triangle

There is right-angled isosceles triangle ABC in which both the length of the sides AB and AC is 12 cm as shown in a figure.

The square PQRS whose length of a diagonal line is 2 cm is in the inside of triangle ABC.

This square moved touching the triangular side within the triangle, while side PS and the side BC had been parallel and it returned to the original position.

In this case, find the area of the portion along which the square passed.

Answer