$$sinx+cosx +sin2x +cos2x=0$$
$$\iff \sqrt{2}sin(x+\dfrac{\pi }{4})+\sqrt{2}sin(2x+\dfrac{\pi }{4})=0$$
$$\iff sin(x+\dfrac{\pi }{4})+sin(2x+\dfrac{\pi }{4})=0$$
$$\iff 2sin(\dfrac{3x}{2}+\dfrac{\pi }{4}).cos\dfrac{x}{2}=0$$
$$\iff \begin{bmatrix}& sin(\dfrac{3x}{2}+\dfrac{\pi }{4})=0 & \\ & cos\dfrac{x}{2}=0 &
\end{bmatrix} \iff \begin{bmatrix} & \dfrac{3x}{2}+\dfrac{\pi }{4}=k\pi & \\ & \dfrac{x}{2}=\dfrac{\pi }{2} +k\pi & \end{bmatrix} ( k \in \mathbb{Z})$$
$$ \iff x=...$$