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**PatternMan****Member**- Registered: 2014-03-08
- Posts: 144

n

------

x - y

= or not =

n+y

------

x

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,382

By ----- do you mean divide?

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 6,092

hi

You only need one counter example to prove it is false. Try choosing some numbers for n, x and y.

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,382

If you do, it's false. Counterexample: n, x is 2, y is 1

2/(2-1) doesn't equal (2+1)/2

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**PatternMan****Member**- Registered: 2014-03-08
- Posts: 144

ShivamS wrote:

If you do, it's false. Counterexample: n, x is 2, y is 1

2/(2-1) doesn't equal (2+1)/2

This is proof by what? So you only need one instance of a counterexample to prove it's false but you need to use variables to prove something is true. Well I found I found some numbers that made it true and I was going to use it to solve a problem but realized that it might not be true for all numbers and turns out it isn't.

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**ShivamS****Member**- Registered: 2011-02-07
- Posts: 3,382

To prove it false, you need only one counterexample. To prove it true, there are several methods like contradiction, induction. A great book on proofs is How to Prove It: A Structured Approach by Daniel J. Velleman.

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