Hi I am not sure what substitution to use for this, have tried $\displaystyle cos(x+x)=cosxcosx-sinxsinx$ and then I tried $\displaystyle cos\theta+cosy=2cos(\frac{x+y}{2})cos(\frac{x-y}{2})$

the question is: find all solutions if $\displaystyle 2cos2x+4sinxcosx=\sqrt{2}$ in the range $\displaystyle o \leq x \leq 2\pi$