Trigonometrymedium · Past Paper
If cos A = 4/5, find cos 2A.
A7/25
B24/25
C-7/25
D16/25
✓ Correct Answer: A — 7/25
cos 2A = 2 cos² A - 1 = 2(16/25) - 1 = 32/25 - 25/25 = 7/25.
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