Тригонометрия
(2cos^2)x=1-sinx

2-2sin²x-1+sinx=0sinx=a2a²-a-1=0D=1+8=9a1=(1-3)/4=-1/2⇒sinx=-1/2⇒x=(-1)^(n+1)*π/6+πn,n∈za2=(1+3)/4=1⇒sinx=1⇒x=π/2+2πk,k∈z