Question

√3 cos2x + 2sinx.cosx = -1

Giúp mình đi ạ 

Answer 1

`\sqrt{3}cos 2x+2sin x cos x=-1`

`<=>\sqrt{3}cos 2x+sin 2x=-1`

`<=>cos(2x-\pi/6)=-1/\sqrt{2}`

`<=>[(2x-\pi/6=[3\pi]/4+k2\pi),(2x-\pi/6=[-3\pi]/4+k2\pi):}`

`<=>[(x=[11\pi]/24+k\pi),(x=[-7\pi]/24+k\pi):}`      `(k in ZZ)`