Sin3x+Sin7x=-Sin11x
Sin3x+Sin7x + Sin11x = 0
(Sin3x + Sin11x) + Sin7x = 0
2Sin7xCos4x + Sin7x = 0
Sin7x(2Cos4x + 1 ) = 0
Sin7x = 0 или 2Сos4x +1 = 0
7x = πn , n ∈ Z Cos4x = -1/2
x = πn/7 , n ∈Z 4x = +-arcCos(-1/2) + 2πk , k ∈Z
4x = +-2π/3 + 2πk , k ∈Z
x = +-π/6 + πk/2 , k ∈ Z