Question

cosx/3=-1/2

Answer 1

$cos frac{x}{3} =- frac{1}{2}$

$frac{x}{3} =$ ± $arccos(- frac{1}{2})+2 pi k,$ $k$ ∈ $Z$

$frac{x}{3}=$ ± $( pi -arccos frac{1}{2})+2 pi k,$  $k$ ∈ $Z$

$frac{x}{3}=$ ± $(pi - frac{ pi }{3} )+2 pi k,$ $k$ ∈ $Z$

$frac{x}{3} =$ ± $frac{2 pi }{3} +2 pi k,$ $k$ ∈ $Z$

$x=$ ± $2 pi +6 pi k,$ $k$ ∈ $Z$