Question

cos2x=2cosx помогите срочно

Answer 1

$COS^{2}(x)- SIN^{2}(x) = 2COS(x) ;$$1- SIN^{2}(x)- SIN^{2}(x)=2COS(x);$
$frac{1-2 SIN^{2}(x) }{2} = COS(x) ;$
$frac{1}{2}- SIN^{2}(x) = COS(x);$
$frac{1}{2}-1+ COS^{2}(x)=COS(x);$
$COS^{2}(x)-COS(x)= frac{1}{2} ;$
$COS(x)(COS(x)-1)=frac{1}{2};$
$1)COS(x) = frac{1}{2}; 2)COS(x)=frac{3}{2} 1) x= frac{ pi }{3}; 2)arccos frac{3}{2}+2 pi$