HINT:
Another way:
$$\cos x-\sin x=\sqrt2\sin\left(\dfrac\pi4-x\right)$$
$$\cos x+\sin x=\sqrt2\cos\left(\dfrac\pi4-x\right)$$
Write $\dfrac\pi4-x=\dfrac\pi2-2y$
$$\sqrt3\sin2y-\cos2y=1\iff2\sqrt3\sin y\cos y=1+\cos2y=2\cos^2y$$
$$\cos y\left(\tan y-\dfrac1{\sqrt3}\right)=0$$