Point P is a point in the square ABCD, connecting PA, Pb and PC. rotate the triangle PAB 90 degrees clockwise around point B to the position of triangle p'cb Let AB be a and Pb be B (b)

Point P is a point in the square ABCD, connecting PA, Pb and PC. rotate the triangle PAB 90 degrees clockwise around point B to the position of triangle p'cb Let AB be a and Pb be B (b)

The results are as follows: S = (1 / 4) a & sup2; π + s △ ABP - [s △ ABP + (1 / 4) B & sup2; π] = (1 / 4) π (A & sup2; - B & sup2;). 2