Answer: A
Step-by-step explanation:
sin∅ = ⅝ in the first quadrant means you have a triangle with a point at the origin with (opposite side / hypothenuse) = ⅝. This means it is 5 units tall and its diagonal side is 8 units long. Using the Pythagorean theorem, if the width of the triangle is x, x²+5²=8², so x²+25=64. This means x²=64-25=39 and x=+√39. Cos∅ would equal the ratio of your adjacent side (width) to your hypothenuse length, so it would be √39 / 8, which is answer choice A.
