Question

Evaluate sin 18 degrees

Answer 1

using trig identities and formulas

Answer 2

yehp

Answer 3

i began with this: sin 18 = cos 72

Answer 4

not exact, i mean in terms of radicals

Answer 5

there is a way with manipulation of the trig identities

Answer 6

\[2\cos ^{2}36 - 1 = \cos 72\]

Answer 7

\[2(1-2\sin ^{2}18)^{2}-1 = \cos 72\]

Answer 8

then im lost

Answer 9

o ok

Answer 10

@Rizags Are you familiar with the trigonometric products, example:
\(\rm sin^2(x)=(1-cos(2x))/2\)
If you apply it twice, you get the above identity, after which you can solve for sin(18)=cos(72)

Answer 11

so input x=36?