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Isosceles triangle...

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Isosceles triangle...

by moonlite » Sat Oct 04, 2008 6:52 am
In isosceles Δ RST, what is the measure of ∠S?
(1) The measure of R is 100◦.
(2) The measure of T is 40◦.

OA is C

If it's an isosceles triangle that means 2 sides are equal so why can't it be D? Please explain. Thanks.
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by kris610 » Sat Oct 04, 2008 6:58 am
I thought it was A. If one angle is 100, the other two must equal 80, each being 40 because the tri is iso.

B is not sufficient as it could be 40 40 100 or 70 70 40.
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by krazy800 » Sat Oct 04, 2008 7:04 am
Agree with u Kris.. the answer should be A
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by 4meonly » Sun Oct 05, 2008 3:49 am
I angree with A
100+S+T=180
S+T=80
S=T=40

if R=100 then it can not be on the base
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Re: Isosceles triangle...

by Natalllllia » Sun Dec 14, 2008 4:06 am
moonlite wrote:In isosceles Δ RST, what is the measure of ∠S?
(1) The measure of R is 100◦.
(2) The measure of T is 40◦.

OA is C

If it's an isosceles triangle that means 2 sides are equal so why can't it be D? Please explain. Thanks.
I met same problem only with diffrent angles

In isosceles Δ RST, what is the measure of ∠R?
(1) The measure of T is 100◦.
(2) The measure of S is 40◦.

OA : A
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by vittalgmat » Sun Dec 14, 2008 12:22 pm
Here is my approach..
WKT (we know that) triangle is isoscles.
=> 2 sides are equal and corr angles are equal as well.

stmt 1.
R = 100deg

So the other two angles are equal coz we cannot have two angles = 100 and still the figure be a triangle.

Sufficient.

Stmt 2.
T = 40

The triangle could be 40-40-100 OR 40-80-80 triangle
so insufficient.

so IMO it is A.
moonlite: pls check the OA ??

Takeaway: If u r given an ISOSCLES triangle, and if one of the angles > 60, then u can figure out all the angles of the triangle.

Also if u r given one of the isoscles side, u can predict the third side using 3rd side = DSS (
Difference between two sides < third Side < Sum of two sides)


HT helps.
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by nhai2003 » Mon Jun 08, 2009 5:35 pm
I agree with Vitalgmat,
THis DS in GMATprep I did this morning.
The OA is A
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