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Intern
Joined: 06 Sep 2018
Posts: 36
GMAT 1: 760 Q50 V44
GMAT 2: 740 Q48 V44

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05 Oct 2018, 11:03
Hi all, apologies, I googled this and couldn't find a convincing answer.

If I know one side and one angle of a triangle, can I assume I can use that to calculate everything else? (Even if it means using law of sines or whatever).

I am asking not because I want to use those rules, but more to understand "sufficiency".

Thank you so much and sorry for the basic question!
Intern
Joined: 04 Sep 2018
Posts: 2

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05 Oct 2018, 13:54
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No, we can’t find out everything from this information. As explanation, consider drawing a line of a defined length. Now make an angle of a defined measure starting from the end of the line. Now, infinite triangles, with variable length of both the remaining sides and angles can be made.

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Intern
Joined: 06 Sep 2018
Posts: 36
GMAT 1: 760 Q50 V44
GMAT 2: 740 Q48 V44

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05 Oct 2018, 14:01
Makes sense thank you!
Manhattan Prep Instructor
Joined: 04 Dec 2015
Posts: 833
GMAT 1: 790 Q51 V49
GRE 1: Q170 V170

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07 Oct 2018, 12:46
1
gmat800live wrote:
Hi all, apologies, I googled this and couldn't find a convincing answer.

If I know one side and one angle of a triangle, can I assume I can use that to calculate everything else? (Even if it means using law of sines or whatever).

I am asking not because I want to use those rules, but more to understand "sufficiency".

Thank you so much and sorry for the basic question!

I've heard this referred to as 'rubber band geometry'. Start with what you know: in this case, one side and one angle.

Then, imagine yourself 'grabbing' one corner of the figure, and 'stretching' or 'squishing' it, like you would with a rubber band. Make sure that the values you know stay the same, but try to move the rest of the figure as much as possible.

If you end up with a figure that's different, then you know that your known values weren't enough to 'fix' the rest of the triangle.
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