Question 1082385
At {{{x=4}}},
{{{g(4)f(4)=4}}}
{{{2*f(4)=4}}}
{{{f(4)=2}}}
and
{{{gf=4}}}
Differentiating implicitly,
{{{g*(df/dx)+f*(dg/dx)=0}}}
So at {{{x=4}}},
{{{2*(df/dx)+2*(1/4)=0}}}
{{{2*(df/dx)=-1/2}}}
{{{df/dx=-1/4}}}