d20ydx202cosxcos3x=
220(cos2x−220cos3x)
220(cos2x+220cos4x)
220(sin2x+220sin4x)
220(sin2x−220sin4x)
y=2cosxcos3x=cos4x+cos2x
d4ydx4=44cos4x+24cos2xd4nydx4n=44ncos4x+24ncos2xd20ydx20=420cos4x+220cos2x