Because ABCD is rectangular.

So angle BAD= angle QBC=90 degrees.

Because PQ is perpendicular to PC

So CPQ angle =90 degrees.

So CPQ angle +QBC angle = 180 degrees.

So q, b, c, p four-point * * * circle.

So Angel ·QBD = Angel ·QCP

Because the angle is not good = angle CPQ=90 degrees.

So the right triangle BAD is similar to the right triangle CPQ (AA).

So: AD/PQ=AB/PC

So: PQ/PC=AD/AB