nKrynka Sinx + 2sinxcosx = cosx + 2cos²x
sinx(1 + 2cosx) - cosx(1 + 2cosx) = 0
(1 + 2cosx)(sinx - cosx) = 0
1)  1 + 2cosx = 0
cosx = - 1/2
x = (+ -)arccos(-1/2) + 2πn, n∈Z
x = (+ -)(π - arccos(1/2)) + 2πn, n∈Z
x = (+ -)(π - π/3) + 2πn, n∈Z
x = (+ -)(2π/3) + 2πn, n∈Z
2)  sinx - cosx = 0    делим на cosx ≠ 0, x ≠ π/2 + πk, k∈Z
tgx - 1 = 0
tgx = 1
x =  π/4 + πm, m∈Z