How do you find the value of $sin15$ using the double or half angle formula?

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Answer 1 · 2016-12-23T17:03:10

sin 15= $(sqrt3 -1)/(2sqrt2)$

Use the identity $cos 2theta= 1- 2sin^2 theta$ and put $theta$ = 15.

Thus $cos 30= 1-2sin^2 15$

$sqrt3 /2= 1-2sin^2 15$

$sin^2 15=1/2 (1-sqrt3 /2)$ = $(2-sqrt3)/4= (4-2sqrt3)/8 = (sqrt3 -1)^2 /8$

sin 15= $(sqrt3 -1)/(2sqrt2)$

How do you find the value of sin15sin15 using the double or half angle formula?