# Friday Funny: What’s wrong with this mathematical proof?  Today’s Friday Funny is something to see if you can remember your high school algebra.

The following mathematical proof suggests that 2 = 1, which would definitely cause some issues with the accounting type people out there.

So the question is:

“What’s wrong with this mathematical proof?”

Here is the proof that 2 = 1:

1. Let a and b be equal non-zero quantities
a = b
2. Multiply both sides by a
a2 = ab
3. Subtract b2 from both sides
a2 – b2 = ab – b2
4. Factor both sides
(a – b)(a + b) = b(a – b)
5. Divide out (ab)
a + b = b
6. Observing that a = b
b + b = b
7. Combine like terms on the left
2b = b
8. Divide by b
2 = 1      QED

If you can explain what is wrong here, then you might help explain why:

• odd <> even
• black <> white
• night <> day

Post your explanations in the comments.

Enjoy

David

This article was originally posted on http://www.winthropdc.com/blog.

## 6 thoughts on “Friday Funny: What’s wrong with this mathematical proof?”

1. Dividing by (a – b) is the same as dividing by 0 since a = b, and you cannot divide by 0.

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2. Wow…I haven’t seen that proof since high-school geometry class…thanks for bringing me back to the good ol’ days! 🙂

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3. Step 5 – take a close look at (a – b) and dividing by it.

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4. You can’t divide by zero!

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