Sin^2 х+sin^2 2 х+sin^2 3 х+sin^4 х=2

(1-cos2x) / 2 + (1-cos4x) / 2 + (1-cos6x) / 2 + (1-cos8x) / 2=2

1-cos2x+1-cos4x+1-cos6x+1-cos8x=4

cos2x+cos4x+cos6x+cos8x=0

2cos5xcos3x+2cos5xcosx=0

2cos5x (cos3x+cosx) = 0

2cos5x*2cos2xcosx=0

cos5x=0⇒5x=π/2+πn⇒x=π/10+πn/5

cos2x=0⇒2x=π/2+πn⇒x=π/4+πn/2

cosx=0⇒x=π/2+πn