If cos A = 12/13, and A is an acute angle, what is the value of sin A?
Correct: A
We use the fundamental trigonometric identity: sin²A + cos²A = 1. Substitute the given value of cos A: sin²A + (12/13)² = 1. sin²A + 144/169 = 1. sin²A = 1 - 144/169. sin²A = (169 - 144) / 169. sin²A = 25/169. sin A = √(25/169) = 5/13. Since A is an acute angle, sin A must be positive.