Dear james_bond,
or if you like the equivavalent:
hint: in [] brackets there is sin(a+b) with suitable a and b.
Hello, james_bond!
Solve the equation: .
Square both sides: .
. . . . . .
. . . . . .
. . . . . . . . . . . . . . .
. . . . . . . . . . . . . .
But we find that half of the roots are extraneous.
The equation is satisfied only if is in Quadrant 1.
Therefore: .