Question 379613
Let {{{N}}} be the number.
{{{f(N)=1/N+4N^2}}}
{{{graph(300,300,-1,9,-1,9,0,1/x+4x^2)}}}
Take the derivative of f(N) and set it equal to zero.
{{{df/dN=-1/N^2+8N}}}
{{{1/N^2=8N}}}
{{{N^3=1/8}}}
{{{highlight(N=1/2)}}}