# Somethings go wrong...

Algebra Level 2

This problem was not created by me.

Let a = b.

$$1.\quad { a }^{ 2 }=ab\\ { 2.\quad a }^{ 2 }-{ b }^{ 2 }={ a }^{ 2 }-ab\\ 3.\quad (a-b)(a+b)=a(a-b)\\ 4.\quad a+b\quad =\quad a\\ 5.\quad b\quad =\quad a\quad =\quad 0$$

So all numbers are equal to 0... What step went wrong? (Try not to take more than 2 minutes.)

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