#1) Don't forget the Product Rule!
f(x)=x^2+1
g(x)=x^3+3
show(diff(f(x),x))
show(diff(g(x),x))
show(diff(f(x)*g(x),x).expand())
show((f(x)*diff(g(x),x)+g(x)*diff(f(x),x)).expand())
p1=plot(f(x)*g(x),0,5,color='red')
p2=plot(diff(f(x)*g(x),x),0,5,color='green')
p1+p2