Answer:
The value of cos theta for 0° < theta < 90° will be 20 / 29
Explanation:
To solve this problem we can express three trig functions as ratios involving the sides of a right-angle triangle, the adjacent side, the opposite side and the hypotenuse. In this case sin θ = a / c, such that a = 21 and c = 29.
By Pythagorean Theorem,

Therefore cos θ = b / c = 20 / 29. This is the cosine ration of the adjacent side over the hypotenuse.