The question is find the general solution of this equation:$$\sin(7\phi)+\cos(3\phi)=0$$
I tried to use the "Sum-to-Product" formula, but found it only suitable for $\sin(a)\pm \sin(b)$ or $\cos(a)\pm \cos(b)$. So I tried to expand $\sin 7\phi$ and $\cos 3\phi$, but the equation became much more complicated..
I'm self studying BUT There's nothing about how to solve this type of equations on my textbook..
reeeaaaaally confused now..