+0  
 
0
692
1
avatar

a=b        /∙a

a^2=ab       /-b^2

a^2-b^2=ab-b^2        factorize

(a-b)(a+b)=b(a-b)       /÷(a-b)

a+b=b        replace the a by a b, as a=b

b+b=b

2b=b         /÷ b

2=1

Q.E.D

Detect the Fallacy

Have fun messing with your friends

 Oct 25, 2015
 #1
avatar+4423 
+5

please

 

first line you set a=b

thus (a-b)=0

 

4th line you divide by (a-b), i.e. you divide by 0.  This is undefined.

 Oct 25, 2015

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