`4sin² x + 4cosx – 1 = 0` `<=> 4(1 – cos² x) + 4cos x – 1 = 0` `<=> 4 – 4cos² x + 4cos x – 1 = 0` `<=>` \(\left[ \begin{array}{l}cos x = \dfrac{3}{2} (l)\\cos x = -\dfrac{1}{2}\end{array} \right.\) `=> cos x = -1/2` `<=> x = ±(2π)/3 + k2π` `(k ∈ ZZ)` Reply
$4\sin^2x+4\cos x-1=0$ $\Leftrightarrow 4-4\cos^2x+4\cos x-1=0$ $\Leftrightarrow -4\cos^2x+4\cos x +3=0$ $\Leftrightarrow \cos x=1,5$ (loại), $\cos x=-0,5$ (TM) $\cos x=-0,5\Leftrightarrow x=\pm\dfrac{2\pi}{3}+k2\pi$ Reply
`4sin² x + 4cosx – 1 = 0`
`<=> 4(1 – cos² x) + 4cos x – 1 = 0`
`<=> 4 – 4cos² x + 4cos x – 1 = 0`
`<=>` \(\left[ \begin{array}{l}cos x = \dfrac{3}{2} (l)\\cos x = -\dfrac{1}{2}\end{array} \right.\)
`=> cos x = -1/2`
`<=> x = ±(2π)/3 + k2π` `(k ∈ ZZ)`
$4\sin^2x+4\cos x-1=0$
$\Leftrightarrow 4-4\cos^2x+4\cos x-1=0$
$\Leftrightarrow -4\cos^2x+4\cos x +3=0$
$\Leftrightarrow \cos x=1,5$ (loại), $\cos x=-0,5$ (TM)
$\cos x=-0,5\Leftrightarrow x=\pm\dfrac{2\pi}{3}+k2\pi$