(sin4x+sinx)+(sin3x+sin2x)=0⇒
2sin(4x+x2)cos(4x−x2)+
+2sin(3x+2x2)cos(3x−2x2)=0
2sin(52x)cos(32x)+2sin(52x)cos(12x)=0
2sin(52x)[cos(32x)+cos(12x)]=0
2sin(52x)2cos(32x+12x2)cos(32x−12x2)=0
4sin(52x)cosxcos(x2)=0.
==>>sin(52x)=0⇒52x=kπ⇒x=25kπ,
cosx=0⇒x=π2+kπ,
cos(x2)=0⇒x2=π2+kπ⇒x=π+2kπ