Question

If tanx= -1/3, cos>0, then how do you find tan2x?

Answer 1

`tan 2x = (2tanx)/(1 - tan^2x)`
This identity comes in handy, you might want to memorize it.
`=(2(-1/3))/(1 - 1/9)`
`=(-2/3)/(8/9)`
`=-2/3(9/8)`
`= -3/4`