Trigonometryhard · Past Paper
Value of sin^2 10 + sin^2 20 + ... + sin^2 90 is:
A4
B4.5
C5
D5.5
✓ Correct Answer: C — 5
Pairs like sin^2 10 + sin^2 80 = 1. There are 4 such pairs plus sin^2 90 = 1 and sin^2 50? No, 10,20,30,40,50,60,70,80,90: 4 pairs + sin^2 90 = 5.
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