Trigonometryhard · Past Paper
If tan A = 1/7 and tan B = 1/3, then cos 2A is equal to:
A24/25
B31/50
C48/50
D7/25
✓ Correct Answer: A — 24/25
cos 2A = (1 - tan² A) / (1 + tan² A) = (1 - 1/49) / (1 + 1/49) = 48/50 = 24/25.
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