Trigonometrymedium · Past Paper
The value of cos 20 cos 40 cos 80 is:
A1/2
B1/4
C1/8
D1/16
✓ Correct Answer: C — 1/8
Using the formula product of cos(2^n theta), the result is sin(2^3 * 20) / (2^3 sin 20) = sin 160 / 8 sin 20 = 1/8.
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