>A quadrilateral ABCD is circumscribed about a circle and
>P,Q,R,S are the points of tangency of sides AB,BC,CD,DA
>respectively.Let a=AB, b=BC, c=CD, d=AD and p=QS, q=PR. Show
>that ac/(p^2)=bd/(q^2)

If you make a simple drawing, you can be sure that: { a=c=p } and that { b=d=q }.

Therefore, it is true for any number a*a/a^2 = 1 .

Using this, you can be sure that each side of the equasion is equal to 1. And, of course, we all know that 1=1.