A solution of the equation $$\cos 4x=-\frac12 ,$$ in $$[0,\pi]$$ is:

$$A) x=\frac{\pi}{3}$$

$$B) x=\frac{\pi}{6} \quad \quad C)\; x=\frac{5\pi}{3} \quad \quad D) \;x=\frac{5\pi}{6}$$

To be honest I am not very good at trigonometry, so if you could explain it to me a little bit how it goes ... thank you

Question

A solution of the equation  $$\cos 4x=-\frac12 ,$$  in $$[0,\pi]$$ is:

$$A) x=\frac{\pi}{3}$$

$$B) x=\frac{\pi}{6}    \quad \quad C)\; x=\frac{5\pi}{3} \quad \quad D) \;x=\frac{5\pi}{6}$$


To be honest I am not very good at trigonometry, so if you could explain it to me  a little bit how it goes ... thank you

anonymous · Answer

4x = -2pi/3 +k.2.pi => x = - pi/6 + k.pi/2 ; 4x = 2pi/3 +k.2.pi
in [0; pi] => x = ..

anonymous · Answer

Still dumb... never mind, I'll talk to my professor, thanks in advance :(

anonymous · Answer

u read equation trigolome , that is basic equation