Question 242344
{{{ f(x)=1/(x+3) }}}
{{{ f(x+h)=1/(x+h+3)}}}
{{{ f(x+h)-f(x)=1/(x+h+3)-1/(x+3)}}}
{{{ f(x+h)-f(x)=(x+3)/((x+3)(x+h+3))-(x+h+3)/((x+3)(x+h+3))}}}
{{{ f(x+h)-f(x)=((x+3)-(x+h+3))/((x+3)(x+h+3))}}}
{{{ f(x+h)-f(x)=(-h)/((x+3)(x+h+3))}}}
{{{ (f(x+h)-f(x))/h=(-1)/((x+3)(x+h+3))}}}
When h-->0, then

{{{ (f(x+h)-f(x))/h=(-1)/((x+3)^2)}}}