If sin θ = 3/5 and θ is acute, then cos θ equals:
A2/5
B5/4
C3/4
D4/5
Answer & Solution
Correct answer: D. 4/5
1. cos²θ = 1 − sin²θ = 1 − 9/25 = 16/25.
2. cos θ = √(16/25) = 4/5 (positive because θ is acute).
3. This is the classic 3-4-5 Pythagorean triple.
_Source: NCERT Class 11 Maths Ch 3 §3.3 Pythagorean Identity_
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