Question 1079891
<pre><b>
{{{A}}}{{{""=""}}}{{{2pi*r(r+h)}}}

Distribute 2<font face=symbol">p</font>r into the parentheses (r+h)
to remove the parentheses:

{{{A}}}{{{""=""}}}{{{2pi*r^2+2pi*rh}}}

Get the term that does not contain h off the right side, by
subtracting 2<font face=symbol">p</font>r<sup>2</sup> from both sides:


{{{A-2pi*r^2}}}{{{""=""}}}{{{2pi*rh}}}

Divide both sides by what is multiplied by h on the right side,
which is 2<font face=symbol">p</font>r

{{{(A-2pi*r^2)/(2pi*r)}}}{{{""=""}}}{{{(2pi*rh)/(2pi*r)}}}

We have to be careful here.  Although it is perfectly correct
to cancel 2<font face=symbol">p</font>r on the right side, since EVERYTHING IS MULTIPLIED.
However, we MUST NOT CANCEL anything on the left side because 
the numerator is a SUBTRACTION, not a MULTIPLICATION.  So 
cancel on the right, but leave the left side as it is.

{{{(A-2pi*r^2)/(2pi*r)}}}{{{""=""}}}{{{(cross(2pi*r)h)/(cross(2pi*r))}}}

{{{(A-2pi*r^2)/(2pi*r)}}}{{{""=""}}}{{{h}}}

Edwin</pre></b>