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Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB = 3BC = 4AC --> we have the ratio of the sides: AB:BC:AC=6:4:3. Now, ALL triangles with this ratio are similar and have the same fixed angles. No matter what these angles actually are, the main point is that we can get them and thus answer the question. Sufficient.

(2) AC^2 + AB^2 > BC^2 --> this condition will hold for equilateral triangle (all angles are 60 degrees) as well as for a right triangle with right angle at B or C (so in this case one angle will be 90 degrees, for example consider a right triangle: AC=5, AB=4 and BC=3). Not sufficient.

Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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02 Aug 2012, 21:46

2

This post received KUDOS

shirisha091 wrote:

Why is the ratio 6:4:3 for AB:BC:AC? Not seeing where the 6 came from.

Divide through the given equality 2AB = 3BC = 4AC by 12 and get \(\frac{AB}{6}=\frac{BC}{4}=\frac{AC}{3}\), which can also be written as AB:BC:AC = 6:4:3.
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PhD in Applied Mathematics Love GMAT Quant questions and running.

Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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01 Aug 2012, 07:07

"(1) 2AB = 3BC = 4AC --> we have the ratio of the sides: AB:BC:AC=6:4:3. Now, ALL triangles with this ratio are similar and have the same fixed angles. No matter what these angles actually are, the main point is that we can get them and thus answer the question. Sufficient."

In reference to Bunnel's explanation -

How can we get the angles from the ratio of the sides? Will the angles be in the same ratio as sides?? This is not true for 45-45-90 and 30-60-90 triangles, the angles do not have the same ratio as the sides? How would you compute the actual angles given the ratio of sides, in statement 1?

Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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01 Aug 2012, 07:14

teal wrote:

"(1) 2AB = 3BC = 4AC --> we have the ratio of the sides: AB:BC:AC=6:4:3. Now, ALL triangles with this ratio are similar and have the same fixed angles. No matter what these angles actually are, the main point is that we can get them and thus answer the question. Sufficient."

In reference to Bunnel's explanation -

How can we get the angles from the ratio of the sides? Will the angles be in the same ratio as sides?? This is not true for 45-45-90 and 30-60-90 triangles, the angles do not have the same ratio as the sides? How would you compute the actual angles given the ratio of sides, in statement 1?

Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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25 Feb 2013, 03:51

(2) AC^2 + AB^2 > BC^2 --> this condition will hold for equilateral triangle (all angles are 60 degrees) as well as for a right triangle with right angle at B or C (so in this case one angle will be 90 degrees, for example consider a right triangle: AC=5, AB=4 and BC=3). Not sufficient.

Bunuel,

Can you please explain the above mentioned statement. I am not able to understand
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(2) AC^2 + AB^2 > BC^2 --> this condition will hold for equilateral triangle (all angles are 60 degrees) as well as for a right triangle with right angle at B or C (so in this case one angle will be 90 degrees, for example consider a right triangle: AC=5, AB=4 and BC=3). Not sufficient.

Bunuel,

Can you please explain the above mentioned statement. I am not able to understand

If AC=AB=BC=1 (satisfies AC^2 + AB^2 > BC^2) --> ABC is an equilateral triangle (all angles are 60 degrees) --> all angles are less than 90 degrees. If AC=5, AB=4 and BC=3 (satisfies AC^2 + AB^2 > BC^2) --> ABC is a right triangle --> NOT all angles are less than 90 degrees.

Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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10 Dec 2013, 09:42

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB = 3BC = 4AC (2) AC^2 + AB^2 > BC^2

A triangle where a^2 + b^2 = c^2 is a right triangle, but is there any way of determining if measures greater than or less than that (say, if a^2 + b^2 was greater than c^2) lead to a triangle having measures greater than or less than 90?

I see how 1 is sufficient. ABC will always have that exact ratio of side lengths. The triangle could be 2x3x4 or 200x300x400 but the angle measurements will always be the same.

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB = 3BC = 4AC (2) AC^2 + AB^2 > BC^2

A triangle where a^2 + b^2 = c^2 is a right triangle, but is there any way of determining if measures greater than or less than that (say, if a^2 + b^2 was greater than c^2) lead to a triangle having measures greater than or less than 90?

I see how 1 is sufficient. ABC will always have that exact ratio of side lengths. The triangle could be 2x3x4 or 200x300x400 but the angle measurements will always be the same.

Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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11 Dec 2013, 05:20

Bunuel wrote:

WholeLottaLove wrote:

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB = 3BC = 4AC (2) AC^2 + AB^2 > BC^2

For a right triangle: \(a^2 +b^2= c^2\). For an acute triangle: \(a^2 +b^2>c^2\). For an obtuse triangle: \(a^2 +b^2<c^2\).

Then wouldn't 2) be sufficient? According to \(a^2 +b^2<c^2\), AC^2 + AB^2 > BC^2 shows that the two legs combined are greater than the third implying that this is an acute triangle.

Are all angles of triangle ABC smaller than 90 degrees?

(1) 2AB = 3BC = 4AC (2) AC^2 + AB^2 > BC^2

For a right triangle: \(a^2 +b^2= c^2\). For an acute triangle: \(a^2 +b^2>c^2\). For an obtuse triangle: \(a^2 +b^2<c^2\).

Then wouldn't 2) be sufficient? According to \(a^2 +b^2<c^2\), AC^2 + AB^2 > BC^2 shows that the two legs combined are greater than the third implying that this is an acute triangle.

No, because we don't know whether BC is the largest side.
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Re: Are all angles of triangle ABC smaller than 90 degrees? [#permalink]

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05 Mar 2015, 10:10

Bunuel, could you explain how we will find angles when we have ratio of sides as in 1). I understand that it will have the same angles, but how can we find them?
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If my post was helpful, press Kudos. If not, then just press Kudos !!!

Bunuel, could you explain how we will find angles when we have ratio of sides as in 1). I understand that it will have the same angles, but how can we find them?

Finding the angles is not our aim (and this is not what you need to know for the GMAT). The aim is to determine whether we CAN find them.
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From your analysis, a^2 + b^2 < c^2 ------------------ (c is largest then obtuse angle) so, 3^2 + 4^2 < 6^2 -------------------- Then we have an obtuse angle.

So statement 1 becomes insufficient, Plz help to clarify....

From your analysis, a^2 + b^2 < c^2 ------------------ (c is largest then obtuse angle) so, 3^2 + 4^2 < 6^2 -------------------- Then we have an obtuse angle.

So statement 1 becomes insufficient, Plz help to clarify....

The question asks: are all angles of triangle ABC smaller than 90 degrees?

Any triangle which has the ratio of the sides 6:4:3, will be an obtuse triangle, and thus we have an YES answer to the question:

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