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# If m and n are the roots of the equation

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If m and n are the roots of the equation [#permalink]  18 Aug 2018, 00:39
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HI guys!

Question:

If m and n are the roots of the equation $$a^2 - 6a + 8 = 0$$, then find the value of $$(m+n)(m-n)$$

A. 12

B. 8

C. 16

D. 4

E.18

Now, the answer should be 12, because the fractioning of the equation gets me (a-4) (a-2). However, what if I switched places here and put (a-2) (a-4). Then, m = 2 and n=4, thus (2+4) (2-4) = -12. Where am I going wrong? Sorry for this stupid question. And btw, roots of the equation are always positive then, right?

Appreciate any help.

Last edited by Carcass on 18 Aug 2018, 02:03, edited 1 time in total.
Edited by Carcass
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Re: If m and n are the roots of the equation [#permalink]  18 Aug 2018, 02:13
Expert's post
Hi,

before to post a question on the board, please, follow the rule fr posting here https://greprepclub.com/forum/rules-for ... -1083.html and how to format a question here https://greprepclub.com/forum/qq-how-to ... -2357.html

Moreover, post the question under the right section and not in general quant section.

Back to the question.

You are right m=2 n=4 in which case the answer is -12

But could be the other way around also: m=4 an n=2 which is 12

No a good question.

Regards
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Re: If m and n are the roots of the equation [#permalink]  18 Aug 2018, 04:46
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Appreciate the comments, Carcass. Sorry for being careless, and thank you for the clarification on the question.

However, I think you made a mistake there. If m=4 and n=2, then (m+n)(m−n) = (4+2) (4-2) = 12. I doesn't make a whole lot of difference though, because I guess we just established that this is not a well-thought-out question.

Thanks!
Re: If m and n are the roots of the equation   [#permalink] 18 Aug 2018, 04:46
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