Question

Simplify the expression by using a double-angle formula.

cos^2(theta/3) - sin^2(theta/3)

Answer 1

use
cos^2 x -sin^2x =cos2x

Answer 2

How this is new for me

Answer 3

I need help please

Answer 4

do u know
cos(a+b)=cosa cosb -sina sinb
now put a=x and b=x
so we have
cos(x+x)=cosx cosx -sinx sinx
or
cos2x =(cosx)^2 -(sinx)^2
or cos2x = cos^2 x -sin^2x

Answer 5

i will try it one moment

Answer 6

so the answer will be cos(2.theta/3) right?

Answer 7

yup

Answer 8

are you sure?

Answer 9

Thanks matricked