1)

2cosx-sinx=3/2cosx+sinx

solve all possible ans of x.

2) I got cosx=-1 and 0.4

i am suppose to find all possible ans of x.

i got 66.4 and 293.6 for the 0.4 already.

but how to slove for the -1? the reference angle is 0 and since cos is negative, it should be in the 2nd and 3rd quarant. and thus i got 90 and 180. however the ans is only 180. why?