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root qs- 700 level, weird solution by mgmat!

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root qs- 700 level, weird solution by mgmat!

by vkb16 » Sat Apr 25, 2009 9:04 am
If sqrt{(x+4)^2} = 3, which of the following could be the value of x – 4?

-11

-7

-4

-3

5

oa is A

-----"MGMAT's solution:-
the expression can be simplified to |x + 4|, and the original equation can be solved accordingly.
If |x + 4| = 3, either x = -1 or x = -7 "-----------

why cant we just take x+4=3 => x= -1, and hence x-4=-5????
why are we taking |x+4| = 3??
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by dmateer25 » Sat Apr 25, 2009 9:26 am
I hope this helps.

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by mkbigmoz » Sat Apr 25, 2009 2:01 pm
You cant simply square the foils. You have to factor them out, then square the result, along with the answer. Then complete, result X = -1, or -7. -7-4 = -11
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Re: root qs- 700 level, weird solution by mgmat!

by vittalgmat » Sun Apr 26, 2009 12:18 am
vkb16 wrote:If sqrt{(x+4)^2} = 3, which of the following could be
why cant we just take x+4=3 => x= -1, and hence x-4=-5????
why are we taking |x+4| = 3??
First of all, the problem is based on a principle which roughly put is:

sqrt(x^2) = |x|.

Therefore, MGMT soln does this. If u know this, the prblm becomes easy.

This problem does not look like a 700 level problem.
The problem is pretty straight forward and involves 2 steps.
IMO, this is a 600 level Q.
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by vkb16 » Sun Apr 26, 2009 12:58 am
this was labeled as 700-800 level my MGMAT CAT..

thanks for the info though...
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