P(9,12): For all intents and purposes, the hypotenuse is "r", the opposite side is "y", and the adjacent side is "x".
x = 9 (from the P(9,12))
y = 12 (also from the point)
Using the Pythagorean Theorem, you find out that r = 15.
Therefore, since cos θ = x/r
cos θ = 9/15 or 3/5
Answer: 3/5