A) b5 = b1*q^4
162 = 2*q^4
81 = q^4
q = 3
б) b7 = b1*q^6
1) cos³x - cosx = 0
cosx*(cos²x - 1) = 0
a) cosx = 0
x₁ = π/2 + πk, k∈Z
b) cos²x - 1 = 0
cos²x = 1
cosx = - 1
x₂ = π + 2πn, n∈Z
cosx = 1
x₃ = 2πm, m∈Z
2) sin²x - 3sinx = 0
sinx(sinx - 3) = 0
a) sinx = 0
x₁ = πk, k∈Z
b) sinx - 3 = 0
sinx = 3 не удовлетворяет условию: IsinxI < 1