Question

∠A is an acute angle in a right triangle.

Answer 1

Cosine = adjacent / hypotenuse
So that means the adjacent side = 15 and the hypotenuse = 17
By Pythagorean Theorem, we know that
opposite^2 = hypotenuse^2 - adjacent^2
opposite^2 = 17^2 - 15^2
opposite^2 = 289 - 225
opposite^2 = 64
opposite side = 8

sine = opposite / hypotenuse
So,
sine A = 8 / 17