Today I was having a bit of a nostalgia moment when I came across an old problem then when I tried to solve it...well lets say it was harder than it seemed.

Anyway the equation was:

And it asked you to find the general form of the solution...

I have tried compound, double angle formulas but to no avail. I can graph it and find some solutions but not how to find a general form equation? Can someone please shoe me how to solve it?

Cheers

Lance

EDIT:: Changed the - to a plus +