Question

Given: `cos(2theta)=3/5` find `sin(theta)`?

Answer 1

We know that

`cos(2theta) = 1 - 2sin^2theta`, so

`3/5 = 1 - 2sin^2theta`

`3/5 - 1 = -2sin^2theta`

`2/5 = 2sin^2theta`

`1/5 = sin^2theta`

`sintheta = +- 1/sqrt(5)`

Depending on the quadrant of `theta`.

Hopefully this helps!