Let < QPR = x Let length side small square be a and large square be b If PA'A is a straight line AB/PC=A ' B ' /PB ' In triangle PD'C' PC ' = D ' C ' cotx = a cotx

Therefore PB ' = a + a cotx

Therefore A ' B ' /PB ' =

a a + a cotx

=

1 1 + cot

In triangle PDC PC = DC cotx = b cotx

Therefore PB = b + b cotx

Therefore AB/PB =

b b + b cotx

=

1 1 + cotx

AB/PC=A ' B ' /PB ' Therefore PAA' is a straight line