Hello,

I have a question regarding a problem that my prof gave me:

x=y

then

x² = xy

x²- y²= xy- y²

(x-y) (x+y) = (x-y) y

x+y= y

y+y=y

2y=y

which would mean that 2=1

Can someoneexplainme where the problem is?

Thanks in adavance!

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- January 26th 2010, 12:38 PM #1

- Joined
- Mar 2009
- Posts
- 2

## 2=1 ?

Hello,

I have a question regarding a problem that my prof gave me:

x=y

then

x² = xy

x²- y²= xy- y²

(x-y) (x+y) = (x-y) y

x+y= y

y+y=y

2y=y

which would mean that 2=1

Can someone**explain**me where the problem is?

Thanks in adavance!

- January 26th 2010, 12:40 PM #2

- Joined
- Nov 2008
- From
- France
- Posts
- 1,458

- January 26th 2010, 12:40 PM #3

- Joined
- Feb 2008
- Posts
- 383

Mathematical fallacy - Wikipedia, the free encyclopedia

Scroll to Division by zero for your question.

- January 26th 2010, 12:41 PM #4

- Joined
- Mar 2009
- Posts
- 2