Hello,

This can be interesting... But i think the second method is strange. We look for the x and y that verify the equation. No x and y will make the denominator infinite (i mean no determined x nor y)...

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- Mar 13th 2008, 08:15 AM #1
## Can we?

Can we simplify the following fraction as :-

and then further simplification....

A friend of mine was contradicting this approach and was saying that if the denominator contains variables then you simply can't do it like this. His solution however was that :-

the solution would be that :-

Either, or

What is the real solution ?

- Mar 13th 2008, 08:24 AM #2

- Mar 13th 2008, 08:35 AM #3

- Mar 13th 2008, 08:49 AM #4

- Mar 13th 2008, 09:03 AM #5

- Mar 13th 2008, 09:35 AM #6

- Mar 13th 2008, 09:46 AM #7

- Mar 13th 2008, 09:55 AM #8

- Mar 13th 2008, 10:25 AM #9

- Mar 18th 2008, 01:18 AM #10

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It's not nonsense, it's a perfectly reasonable question about limits. If you let either x or y approach either positive or negative infinity, the denominator will approach positive infinity. How that effects the overall fraction depends more specifically on how you choose x and y.

On the original question, your solution does leave a step unstated, I'm not sure whether you skipped it or not. In cancelling out the denominator, you make the assumption that it isn't zero. In the real numbers, it can't be, since it has to be at least 2, but on similar problems that could cause mistakes. If there was any chance it could be zero, it would be better to deal with that case explicitly.

- Mar 18th 2008, 01:25 AM #11

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Going back over the limit question more carefully, I see that there's no well-defined value of the fraction when both x and y tend to infinity. Following two different paths, you can get two different answers. Setting x=y and taking the limit as x->oo gives 2, but setting x=3y and taking the same limit gives 9/5.