Question 968480
During the time, {{{dt}}}, 
{{{dV/dt=(V(t+dt)-V(t))/dt}}}
{{{V(t+dt)=5(t+dt)(2-(t+dt))}}}
{{{V(t+dt)=(5t+5dt)(2-t-dt)}}}
{{{V(t+dt)=(10t-5t^2-5tdt)+(10dt-5tdt-5(dt)^2)}}}
{{{V(t+dt)=10t-5t^2-10tdt+10dt-5(dt)^2}}}
So then,
{{{V(t+dt)-V(t)=10t-5t^2-10tdt+10dt-5(dt)^2-10t-5t^2}}}
{{{V(t+dt)-V(t)=-10tdt+10dt-5(dt)^2}}}
and,
{{{(V(t+dt)-V(t))/dt=-10t+10-5dt}}}
But {{{dt}}} becomes infinitesimally small so,
{{{(V(t+dt)-V(t))/dt=-10t+10}}}
{{{dV/dt=-10t+10}}}