How do i work this problem out 16x to the 5th power-36x to the 4th power+14x to the 3rd power

Find the length of the following tangent segments to the circles centered at o and o' whose radii are 5 and 3 respectively and the distance between o and o' is 12. what is the tangent segment of cd?

Given that ot =5, xt=12, and ox= 13 is xy tangent to circle o at t? explain.

In the polynomial below, what number should replace the question mark to produce a difference of squares? x2 + ? x - 36