Question 992569
<pre>
a = b               <--a and b can stand for the same quantity. 
aČ = ab             <--we can multiply both sides by a.  
aČ - bČ = ab - b2   <--we can subtract bČ from both sides.
(a-b)(a+b) = b(a-b) <--we factor both sides of the equation.
<font color="red"><b>a+b = b             <--we divide both side by (a-b)</font></b>
b+b = b             <--since a = b, we can substitute b for a
2b = b              <--combine like terms b+b and get 2b
2 = 1               <--we divide both sides by b 
                 

The fallacy is in the step colored red. Since a=b, (a-b)=0 and
we may never divide by 0, even when it's camouflaged as (a-b).

Edwin</pre>