Calc

I'm feeling retarded and need halp:
lim x->0 sin4x/sin6x=?
also
Given y=sin2x-2sinx, find dy/dx=0
also
Given f(x)=xg(x^2), find f'' in terms of g,g',g''
Any help would be much appreciated!

Why not let the computers do the work?


limit(sin(4*x)/sin(6*x), x=0);
                                      2/3

diff(x*g(x^2), x$2);
                               2         3   (2)      2
                       6 D(g)(x ) x + 4 x  (D   )(g)(x )