Van Aubel's theorem

Each square is connected, and the center is lined.

PR and SQ is vertical, and they are symmetry.

AB=2a, BC=2b, CD=2c, DA=2d, and they are complex numbers.

2a+2b+2c+2d=0

∴

a+b+c+d=0

You see the complex number, so A=0. Then, AP=p is z.

∴

p=a+ia=(1+i)a

You see Euler's formula.
π/2=90°

Then, you turn around squares.

SQ=A and PR=B

B=iA

iB=i^2A

∴

A+iB=0

Squares are curved.