GMAT Math : DSQ: Calculating the length of the side of an equilateral triangle

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Example Question #1 :Equilateral Triangles

Isan equilateral triangle?

Statement 1:

Statement 2:, andis equiangular.

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

If, then

.

This makesan equiangular triangle.

If, andis equiangular, then, since corresponding angles of similar triangles are congruent,has the same angle measures, and is itself equiangular.

From either statement, since all equiangular triangles are equilateral, we can draw this conclusion about.

Example Question #2 :Equilateral Triangles

True or false:is equilateral.

Statement 1: The perimeter ofis.

Statement 2:.

Possible Answers:

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question.

Explanation:

The two statements together provide insufficient information. A triangle with sides,, andis equilateral and has perimeter;一个三角形with sides,, andis not equilateral and has perimeter.

Example Question #1 :Dsq: Calculating The Length Of The Side Of An Equilateral Triangle

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is the height of. What is the length of?

(1)

(2)

Possible Answers:

Each statement alone is sufficient

Both statements together are sufficient

Statement 1 alone is sufficient

Statements 1 and 2 together are not sufficient

Statement 2 alone is sufficient

Correct answer:

Statements 1 and 2 together are not sufficient

Explanation:

To find the answer we should know more about the characteristics of the triangle, i.e. its angles, sides...

Statement 1 alone is obviously insufficient, since we don't know whether the triangle is equilateral, nothing can be said about AB.

Statement 2 is equally as unhelpful as statement 1, since we don't know whether ABC is of a specific type of triangle.

Taken together, these statements allow us to calculate the length of CB, but we can't go further, because we don't know what is AD.

Therefore statements 1 and 2 are not sufficient even taken together.

Example Question #4 :Equilateral Triangles

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ABC is an equilateral triangle inscribed in the circle. What is the length of side AB?

(1) The area of the circle is

(2) The perimeter of triangle ABC is

Possible Answers:

Both statements together are sufficient

Statment 2 alone is sufficient

Each statement alone is sufficient

Statements 1 and 2 together are not sufficient

Statement 1 alone is sufficient

Correct answer:

Each statement alone is sufficient

Explanation:

To find the length of the side, we would need to know anything about the lengths in the circle or in the triangle.

From statement 1, we can find the radius of the circle, which allows us to calculate the height of the triangle, since the radius is的高度。最后由于三角形是equilateral, we can also calculate the length of the sides from the height.

Therefore statement 1 is sufficient.

Statement 2 also gives us useful information, indeed the perimeter is simply three times the length of the sides.

Therefore the final answer is each statement alone is sufficient.

Example Question #5 :Equilateral Triangles

Find the side length of.

I)周边的.

II)is equal towhich is.

Possible Answers:

Neither statement is sufficient to answer the question. More information is needed.

Both statements are needed to answer the question.

Statement I is sufficient to answer the question, but statement II is not sufficient to answer the question.

Either statement is sufficient to answer the question.

Statement II is sufficient to answer the question, but statement I is not sufficient to answer the question.

Correct answer:

Both statements are needed to answer the question.

Explanation:

I) Tells us the perimeter of the triangle.

II) Tells us that FHT is an equilateral triangle.

Taking these statements together we are able to find the side length by dividing the perimeter from statement I, by 3 since all side lengths of an equilateral are the same by statement II.

Example Question #6 :Equilateral Triangles

Given equilateral triangleand right triangle, which, if either, is longer,or?

Statement 1:

Statement 2:is a right angle.

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. Since all three sides ofare congruent - specifically,- and, it follows by transitivity that. However, no information is given as to whetherhas length greater then, equal to, or less than, so which ofand, if either, is the longer cannot be answered.

Assume Statement 2 alone. Sinceis the right angle of,is the hypotenuse and this the longest side, soand. However, no comparisons with the sides ofcan be made.

Now assume both statements are true.as a consequence of Statement 1, andas a consequence of Statement 2, so.

Example Question #7 :Equilateral Triangles

What is the length of sideof equilateral triangle?

Statement 1:is a diagonal of Rectanglewith area 30.

Statement 2:is a diagonal of Squarewith area 36.

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

An equilateral triangle has three sides of equal measure, so if the length of any one of the three sides can be determined, the lengths of all three can be as well.

Assume Statement 1 alone.is a diagonal of a rectangle of area 30. However, neither the length nor the width can be determined, so the length of this segment cannot be determined with certainty.

Assume Statement 2 alone. A square with area 36 has sidelength the square root of this, or 6; its diagonal, which is, has lengthtimes this, or. This is also the length of.

Example Question #8 :Equilateral Triangles

What is the length of sideof equilateral triangle?

Statement 1:,, andare all located on a circle with area.

Statement 2: The midpoints of all three sides are located on a circle with circumference.

Possible Answers:

BOTH statements TOGETHER are insufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

We demonstrate that either statement alone yields sufficient information by noting that the circle that includes all three vertices of a triangle - described in Statement 1 - is its circumscribed circle, and that the circle that includes all three midpoints of the sides of an equilateral triangle - described in Statement 2 - is its inscribed circle. We examine this figure below, which shows the triangle, both circles, and the three altitudes:

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The three altitudes intersect at, which divides each altitude into two segments whose lengths have ratio 2:1.is the center of both the circumscribed circle, whose radius is, and the inscribed circle, whose radius is.

Therefore, from Statement 1 alone and the area formula for a circle, we can findfrom the areaof the circumscribed circle:

From Statement 2 alone and the circumference formula for a cicle, we can findfrom the circumferenceof the inscribed circle:

By symmetry,is a 30-60-90 triangle, and either way,, and.

Example Question #9 :Equilateral Triangles

给定两个等边三角形and, which, if either, is greater,or?

Statement 1:

Statement 2:

Possible Answers:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

An equilateral triangle has three sides of equal length, soand.

Assume Statement 1 alone. Since, then, by substitution,.

Assume Statement 2 alone. Since, it follows that, and again by substitution,.

Example Question #10 :Equilateral Triangles

You are given two equilateral trianglesand.

Which, if either, is greater,or?

Statement 1: The perimeters ofandare equal.

Statement 2: The areas ofandare equal.

Possible Answers:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone, and letbe the common perimeter of the triangles. Since an equilateral triangle has three sides of equal length,and, so.

Assume Statement 2 alone, and letbe the common area of the triangles. Using the area formula for an equilateral triangle, we can note that:

and,

so

.

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