GMAT Math : Right Triangles

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #371 : Geometry

 is a right triangle. Evaluate .

Statement 1:  and 

Statement 2:  is not a 30-60-90 triangle.

Possible Answers:

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

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:

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

Explanation:

Statement 1 alone gives insufficient information.  and , but it is not clear which of the three sides is the hypotenuse of .  is not the longest side, so we know that  or  is the hypotenuse, and the other is the second leg. We explore the two possibilities:

If  is the hypotenuse, then the legs are  and ; since the lengths of the legs are 12 and 24, by the Pythagorean Theorem,  has length

.

If  is a leg, then the hypotenuse, being the longest side, is , and  is the other leg; by the Pythagorean Theorem,  has length

.

Statement 2 alone gives insufficient information in that it only gives information about the angles, not the sides.

Assume both statements are true. If  is the hypotenuse and  is a leg, then, since the hypotenuse measures twice the length of a leg from Statement 1, the triangle is 30-60-90, contradicting Statement 2. Therefore, by elimination,   is the hypotenuse, and, consequently, .

Example Question #12 : Dsq: Calculating The Length Of The Side Of A Right Triangle

Given  is a right triangle, which side is the hypotenuse - , 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.

EITHER 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.

BOTH statements TOGETHER are insufficient 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:

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

Explanation:

Since we are comparing angles, we need to identify the angle of greatest measure; in a right triangle, the angle of greatest measure is the right angle, and the side opposite it is the hypotenuse.

Statement 1 is insufficient, since we can eliminate only angle  as the right angle, and, subsequently, only  as the hypotenuse. Similarly, Statement 2 is insufficent, since we can eliminate only angle  as the right angle, and, subsequently, only  as the hypotenuse. But if we are given both statements, we can eliminate  and  as the hypotenuse, leaving  as the hypotenuse.

Example Question #492 : Data Sufficiency Questions

 has right angle  has right angle . Which, if either, is longer,  or ?

Statement 1: 

Statement 2: 

Possible Answers:

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.

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.

BOTH statements TOGETHER are insufficient to answer the question. 

Correct answer:

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

Explanation:

We are being asked to compare the lengths of the hypotenuses of the two triangles, since  and  are the sides opposite the right angles of their respective triangles.

Assume Statement 1 alone. We have that , and , both being right angles, thereby establishing congruence between two pairs of sides and a pair of included angles. By the Side-Angle-Side Theorem, , and, consequently  and  have equal length.

Assume Statement 2 alone. We are only given information about the angle measures, but nothing about the lengths of the sides - actual lengths or comparisons. We can make no conclusions about which hypotenuse is longer.

Example Question #491 : Data Sufficiency Questions

 is a right triangle with right angle . Evaluate .

Statement 1:  has area 24.

Statement 2:  can be circumscribed by a circle with area .

Possible Answers:

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.

EITHER 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:

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

Explanation:

Since  is given as the right angle of the triangle , we are being asked to evaluate the length of hypotenuse .

Statement 1 alone gives insufficient information. We note that the area of a right triangle is half the product of the lengths of its legs, and we examine two scenarios:

Case 1: 

The area is 

By the Pythagorean Theorem, hypotenuse  has length

Case 2: 

The area is 

By the Pythagorean Theorem, hypotenuse  has length

Both triangles have area 24 but the hypotenuses have different lengths.

 

Assume Statement 2 alone. A circle that circumscribes a right triangle has the hypotenuse of the triangle as one of its diameters, so the length of the hypotenuse is the diameter - or, twice the radius - of the circle. Since the area of the circumsctibed circle is , its radius can be determined using the area formula:

The diameter - and the length of hypotenuse  - is twice this, or 10.

Example Question #492 : Data Sufficiency Questions

 is a right triangle. Evaluate .

Statement 1:  and 

Statement 2:  has a  angle.

Possible Answers:

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. 

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.

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 we do not know whether  is the hypotenuse or a leg of , we can show that  can take one of two different values.

Case 1: If  is the hypotenuse, then the legs are  and ; since their lengths are 10 and 20, by the Pythagorean Theorem,  has length

.

Case 2: If  is a leg, then the hypotenuse, being the longest side, is , and  is the other leg; by the Pythagorean Theorem,  has length

.

Statement 2 gives insufficient information, since it only clues us in to the measures of the angles, not the sides.

Now assume both statements. Since one of the angles of the right triangle has measure , the other has measure ; the triangle is a 30-60-90 triangle, and therefore, its hypotenuse has twice the length of its shorter leg. Since, from Statement 1,  is the hypotenuse, and  is the longer leg, the length of which, by the 30-60-90 Theorem, is  times that of shorter leg , or .

Example Question #495 : Data Sufficiency Questions

Right_triangle_1

Refer to the above figure. What is the length of  ?

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.

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

BOTH statements TOGETHER are insufficient 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.

Correct answer:

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

Explanation:

As each statement alone only gives the length of one segment, neither statement alone is sufficient to find the length of any other segment, including, in particular, .

Assume both statements to be true.  can be found by way of the Pythagorean Theorem:

Now note that  is the altitude of the right triangle from the vertex of the right angle, which divides the right triangle into two triangles similar to each other and the large triangle. Specifically,

By similarity, 

.

 

Example Question #131 : Triangles

Given  is a right triangle, which side is the hypotenuse - , or  ?

Statement 1: 

Statement 2: 

Possible Answers:

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.

EITHER 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:

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

Explanation:

The hypotenuse of a right triangle is its longest side. From Statement 1 alone, we can eliminate only   as the hypotenuse, and from Statement 2 alone, we can eliminate only  . From Statements 1 and 2 together, we can eliminate both, leaving  as the hypotenuse.

Example Question #31 : Right Triangles

 is a right triangle with right angle . Evaluate .

Statement 1:  can be inscribed in a circle with circumference .

Statement 2:  can be inscribed in a cricle with area .

Possible Answers:

EITHER 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.

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.

Correct answer:

BOTH statements TOGETHER are insufficient to answer the question.

Explanation:

From Statement 1 alone, the circumscribed circle has as its diameter the circumference  divided by , or 20. From Statement 2 alone, the circle has area , so its radius can be found using the area formula;

The diameter is the radius doubled, which here is 20.

The hypotenuse of a right triangle is a diameter of the circle that circumscribes it, so the diameter of the circle gives us the length of the hypotenuse. However, we are looking for the length of a leg, . Either statement alone gives us only the length of the hypotenuse, which, without other information, does not give us any further information about the right triangle.

Example Question #12 : Dsq: Calculating The Length Of The Side Of A Right Triangle

Given  is a right triangle, which side is the hypotenuse - , or  ?

Statement 1: 

Statement 2: 

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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. The hypotenuse of a right triangle is longer than either of its two other sides; since  and   are equal in length, neither is the hypotenuse. This leaves  as the hypotenuse.

Assume Statement 2 alone. Since , neither can be the right angle. Therefore,  is the right angle, and its opposite side, , is the hypotenuse.

Example Question #143 : Triangles

Given  and , which, if either, is the longer of the two:  or ?

Statement 1: 

Statement 2:  is a right angle and  is an obtuse angle

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 sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Statement 1 alone gives insufficient information, as it only establishes congruence between two pairs of corresponding sides; without a third congruence or noncongruence between sides or angles, it cannot be established whether the triangles themselves are congruent. Statement 2 alone is insufficient, since it only compares two angles without giving any information about sidelengths, whether absolute or relative.

Assume both statements to be true. From Statement 1, we have the congruence statements  and , and from Statement 2, we have that the included angle  from  has measure , and that the included angle  from , being obtuse, has, by definition, measure greater than this. This sets up the conditions of the Side-Angle-Side Inequality Theorem, or Hinge Theorem, which states that in this situation, the third side opposite the greater angle is longer than the third side opposite the lesser. Therefore, it can be deduced that .

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