Question

cos36?

Answer 1

really ?

Answer 2

without calcy ?

Answer 3

first can u find sin 18 without calcy ?

Answer 4

noo :/

Answer 5

pretty standard

Answer 6

let x= 18
5x = 90
3x = 90-2x
now take sin on both sides.

Answer 7

sin 3x = sin(90-2x)
sin 3x = cos 2x

Answer 8

now put the formula fo sin 3x and cos 2x in terms of powers of sin x only.

Answer 9

u get a cubic in sin x. solve it.

Answer 10

wait,theres a formula for sin3x? :P

Answer 11

absolutely.

Answer 12

:O

Answer 13

sin 3x = 3sin x - 4 sin^3 x

Answer 14

okay yes ! i remember :P

Answer 15

thanks!

Answer 16

okay I guess i can do it now

Answer 17

from sin 18, u get cos 36
from the formula of cos 2x in terms of sin x

Answer 18

good :)

Answer 19

:D