Question 898780
{{{"f(a)"}}}{{{""=""}}}{{{3/a}}}
{{{"f(a+h)"}}}{{{""=""}}}{{{3/(a+h)}}}
{{{"f(a+h)"-"f(a)"}}}{{{""=""}}}{{{3/(a+h)-3/a}}}
<pre>
Before you go further and divide by h, get an LCD of a(a+h):

{{{"f(a+h)"-"f(a)"}}}{{{""=""}}}{{{(3a-3(a+h))/(a(a+h))}}}

{{{"f(a+h)"-"f(a)"}}}{{{""=""}}}{{{(3a-3(a+h))/(a(a+h))}}}

{{{"f(a+h)"-"f(a)"}}}{{{""=""}}}{{{(3a-3a-3h)/(a(a+h))}}}

{{{"f(a+h)"-"f(a)"}}}{{{""=""}}}{{{(-3h)/(a(a+h))}}}

Now divide the left side by h and multiply the right side by {{{1/h}}},
which is really doing the same thing to both sides:

{{{("f(a+h)"-"f(a)")/h}}}{{{""=""}}}{{{expr((-3h)/(a(a+h)))*expr(1/h)}}}

{{{("f(a+h)"-"f(a)")/h}}}{{{""=""}}}{{{expr((-3cross(h))/(a(a+h)))*expr(1/cross(h))}}}

{{{("f(a+h)"-"f(a)")/h}}}{{{""=""}}}{{{-3/(a(a+h))}}}

Edwin</pre>