If $$\sin 6\theta + \sin 4\theta + \sin 2\theta = 0$$, then the general value of $$\theta$$ is

If $$\sin \theta = {{2t} \over {1 + {t^2}}}$$ and $$\theta$$ lies in the second quadrant, then cos $$\theta$$ is equal to

The number of solutions of $$2\sin x + \cos x = 3$$ is

Let $$\tan \alpha = {a \over {a + 1}}$$ and $$\tan \beta = {1 \over {2a + 1}}$$ then $$\alpha + \beta $$ is