PQ is a diameter of a circle and AB is a perpendicular chord cutting it at N. Prove that PN is equal in length to the perpendicular from P on to the tangent at A.

I have attached a diagram of how i imagine this situation to look. If my diagram is correct and I'm supposed to be proving that the two yellow segments are equal, then I'm not sure how to prove this.

However, if my diagram is wrong could someone please correct it so i can visulaise the situation.

Cheers