2sin x cos x = cos x 

2sin x cos x = cos x ОДЗ: x∈R2sinx*cosx-cosx=0cosx(2sinx-1)=0[cosx=0;          [x=П/2+Пn; n∈Z[2sinx-1=0;      [x=(-1)^n П/6+Пn;n ∈Z

2sin x cos x = cos x 2sin x cos x-cos x=0/cos x2tdx-1=02tgx=1tgx=1/2x=arctg1/2+пn