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# If the length of side AB is 17, is triangle ABC a right

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If the length of side AB is 17, is triangle ABC a right [#permalink]  24 Jul 2007, 18:06
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50% (01:58) correct 50% (01:06) wrong based on 1 sessions
If the length of side AB is 17, is triangle ABC a right triangle?

(1) The length of side BC is 144.

(2) The length of side AC is 145.

Can someone explain what would be correct answer for this?
Intern
Joined: 10 Jun 2007
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Can this be even be a triangle?
I may be wrong but my answer is E.
Director
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Re: DS Question [#permalink]  24 Jul 2007, 18:55
a3d wrote:
If the length of side AB is 17, is triangle ABC a right triangle?

(1) The length of side BC is 144.

(2) The length of side AC is 145.

Can someone explain what would be correct answer for this?

This was a good one .
Instead of calculating squares ( which gmat will never ask you ) , I did a quick calculation ie 145^2 - 144^2 = (145-144)(145 +144 ) = 289
which is square of 17.
So it does means a triangle with 17 144 145 is right angle triangle . But this does not mean that answer is C . But now if we know that one of side 144 or 145 it has to be a right angle triangle .
Intern
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Statement 1 Insuff
Statement 2 Insuff

Combining, is 17^2 +144^2=145^2?

for 2 consecutive mumbers, the difference in their squares= n1+n2
therefore 144^2-145^2=289=17^2

therefore the triangle has to be RtAng

Therefore c
Senior Manager
Joined: 21 Jun 2006
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C

by knowing one side is 145 tells you nothing of the shape of the triangle.
For all we know it could be close to a straight line.

similar with option B

combine A and B and use pythogarus to see if it adds up.
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Re: DS Question [#permalink]  25 Jul 2007, 01:18
ashkrs wrote:
a3d wrote:
But this does not mean that answer is C . But now if we know that one of side 144 or 145 it has to be a right angle triangle .

Why do u say that? My original answer was C. But I gave this a thought after reading ur answer but decided, just knowing two sides and no angles would be useless.
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Re: DS Question [#permalink]  25 Jul 2007, 08:49
ioiio wrote:
ashkrs wrote:
a3d wrote:
But this does not mean that answer is C . But now if we know that one of side 144 or 145 it has to be a right angle triangle .

Why do u say that? My original answer was C. But I gave this a thought after reading ur answer but decided, just knowing two sides and no angles would be useless.

It is simply impossible to conclude on the type of a triangle by knowing just 2 sides. It has to be C
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It has to be C. And, to save time, there is no need to calculate if it is a right triangle or not.

1) Ins. - you know 2 sides, no angles

2) Ins. - same reasoning

Together you have 3 sides and it either follows the pythagreon theorem or doesn't. The answer doesn't matter if its yes or no, just if it can be solved.
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emoryhopeful wrote:
It has to be C. And, to save time, there is no need to calculate if it is a right triangle or not.

1) Ins. - you know 2 sides, no angles

2) Ins. - same reasoning

Together you have 3 sides and it either follows the pythagreon theorem or doesn't. The answer doesn't matter if its yes or no, just if it can be solved.

ah. the more of these I read the more these make sense.

I was leaning to E becasue of the lack of angles.
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emoryhopeful wrote:
It has to be C. And, to save time, there is no need to calculate if it is a right triangle or not.

1) Ins. - you know 2 sides, no angles

2) Ins. - same reasoning

Together you have 3 sides and it either follows the pythagreon theorem or doesn't. The answer doesn't matter if its yes or no, just if it can be solved.

Great answer! I need to remember that for a DS all you need to know is whether or not you can solve it (or answer the yes/no question). The less actual math to do, the better!
Director
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I agree with ashkrs
This is a righ angle triangle
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I'm inclinced to take C here, because you don't know the shape of a triangle with just one side given.

With both, you can quickly test if it fits pythagora's theorem.
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Re: DS Question [#permalink]  26 Jul 2007, 05:39
a3d wrote:
If the length of side AB is 17, is triangle ABC a right triangle?

(1) The length of side BC is 144.

(2) The length of side AC is 145.

Can someone explain what would be correct answer for this?

I get C as well. No calculation needed.. just definition/rules of triangles.
Re: DS Question   [#permalink] 26 Jul 2007, 05:39
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