решите уравнение
cosквадрат5x=1/4

cos²5x=1/4(cos5x-√2/2)(cos5x+√2/2)=0cos5x=√2/2  5x=+-π/4+2πk,k∈Zcos5x=-√2/2 5x=+-3π/4+2πk, k∈Zx₁=+-π/20+2πk/5,k∈Zx₂=+-3π/20+2πk/5, k∈Z