Question

Question #09851

Answer 1

`tan50-tan40`

`=tan50-tan(90-50)`

`=tan50-cot50`

`=tan50-1/tan50`

`=(tan^2 50-1)/tan50`

`=(-2(1-tan^2 50))/(2tan50)`

`=-2/tan100`

`=-2cot100`

`=-2cot(90+10)`

`=2tan10`

So `tan50=tan40+2tan20`