First slide

Trigonometric Identities

Question

$\sin^{2} 5^{0} + \sin^{2} 10^{0} + \sin^{2} 15^{0} - - - - \sin^{2} 180^{0} =$

Moderate

A

9
B

12
C

18
D

24

Solution

sin² 5⁰ + …….. + …… + sin²175 $°$ +0
= 2(sin²5+….. + sin²85⁰) + sin² 90⁰+2sin²45⁰
(if A + B = 90⁰ then sin²A +sin²B=1)
= 2(8) + 1+ 1 = 18

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