Hello, just another problem my tutuor set me.

A square ABCDwith sides of length 1 be given. A point Xon BC is at distance d

fromC, and a point Y on CD is at distance d from C. The extensions of: AB and DX

meet atP, AD and BY meet at Q, AX and DC meet at R, and AY and BC meet at

S. If points P, Q, R and S are collinear, figure out the value 'd'.

Cheers