Let y=sin(x)sin(2x)sin(3x).
sin(2x)=2sin(x)cos(x);
sin(3x)=sin(2x)cos(x)+cos(2x)sin(x)=
2sin(x)cos2(x)+sin(x)-2sin3(x)=
2sin(x)-2sin3(x)+sin(x)-2sin3(x)=
3sin(x)-4sin3(x)=sin(x)(3-4sin2(x)).
y=2sin3(x)cos(x)(3-4sin2(x)),
y=6sin3(x)cos(x)-8sin5(x)cos(x).
dy/dx=18sin2(x)cos2(x)-6sin4(x)-40sin4(x)cos2(x)+8sin6(x),
dy/dx=18sin2(x)-18sin4(x)-6sin4(x)-40sin4(x)+40sin6(x)+8sin6(x),
dy/dx=18sin2(x)-64sin4(x)+48sin6(x);
d2y/dx2=36sin(x)cos(x)-256sin3(x)cos(x)+288sin5(x)cos(x).