i am getting -2 + √3 .
what problem are you having .
if α=330°,then using the formula tanα=2tanα/2/1-tan2α/2 find the value of tanα/2 ?
see the thing to keep in mind here is that you get a quadratic in tan (a/2)
so the problem is that this willl give 2 roots..
You have to take the -ve root.. because a/2 lies between 90 and 180 (165 precisely)
Hence you can ignore the +ve root.