znanija.com/task/35217707
sin(5x) - sin(x) = sin(7x) - sin(3x) ⇔2sin(2x)*cos(3x) = 2sin(2x)*cos(5x) ⇔
2sin(2x) *( cos(3x) - cos(5x) ) =0 ⇔2sin(2x) *2sin(x)*sin(4x) = 0 ⇔
4sin(4x)*sin(2x) *sin(x) = 0
sin4x = 0 ⇒ 4x = πn ⇔ x =(π/4)n , n ∈ ℤ
* * * * * P.S.
sinα - sinβ =2sin((α -β)/2) *cos((α +β)/2)
sin(2α =2sinα*cosα ; sin4α =2sin2α*cos2α= 4sinα*cosα*cos2α