Given that sin θ = m/n, where θ is an acute angle, what is cos θ?
Correct: A
We use the identity sin²θ + cos²θ = 1. Substitute sin θ = m/n: (m/n)² + cos²θ = 1. m²/n² + cos²θ = 1. cos²θ = 1 - m²/n². To subtract, find a common denominator: cos²θ = (n² - m²) / n². Since θ is acute, cos θ is positive. So, cos θ = √((n² - m²) / n²) = √(n² - m²) / n.