Question

is there any equivalent number of sine so that i can solve sine 70 without using any calculator? tnx

Answer 1

sin 3x = 3sin x - 4 sin^3x
so sin 210 = 3 sin 70 - 4sin^3 70
=>-sin 30 = 3 sin70 - 4sin^3 70
-> 8sin^3 70 - 6sin 70 -1 =0
let sin70 =x
=> 8x^3 - 6x -1 =0
that'd now require some higher mathematical skill to solve it..but you dont have to use much of calculator ;)

Answer 2

i'm sorry, but how did you get sin 3x = 3sin x - 4 sin^3x ? thank you :)

Answer 3

thats a universal formulla ..
you may derive it through many paths
here's one
note that sin(a+b) = sina cosb + cosa sinb
will this help ?

Answer 4

oh i see,
thank you :)
it help me so much :))

Answer 5

glad to help ^_^