GMAT Math : DSQ: Calculating an angle in a right triangle

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Example Question #1 : Dsq: Calculating An Angle In A Right Triangle

Which interior angle of $\Delta ABC$ has the greatest measure?

Statement 1: $\left (AB \right )^{2} + \left (BC \right )^{2} =\left (AC \right )^{2}$

Statement 2: $\angle B$ is a right angle.

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.

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 insufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

If Statement 1 is assumed, then by the converse of the Pythagorean Theorem, the triangle is a right triangle with right angle $\angle B$ , which is explicitly stated in Statement 2. If $\angle B$ is a right angle, then the other two angles are acute, since a triangle must have at least two acute angles. A right angle measures $90 ^{\circ }$ and an acute angle measures less, so from either statement, we can deduce that $\angle B$ is the angle with greatest measure.

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Example Question #2 : Dsq: Calculating An Angle In A Right Triangle

Triangle

Note: Figure NOT drawn to scale.

$\angle A,\angle B$ are acute. Is $\angle C$ a right angle?

Statement 1: $m \angle A + m \angle B <90 ^{\circ }$

Statement 2: c = 260

Possible Answers:

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.

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.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

A right triangle must have its two acute angles complementary; if Statement 1 is assumed, then this is false, the triangle is not a right triangle, and $\angle C$ is not a right angle.

If Statement 2 is assumed, then we apply the converse of the Pythagorean Theorem to show that the triangle is not right. The sides of a triangle have the relationship

$c^{2} = a^{2} + b^{2}$

only in a right triangle. If c = 260 , then the statement to be tested would be

$260^{2} = 70^{2} + 240^{2}$

67,600 =4,900 + 57,600

67,600 =62,500

This statement is false, so the triangle is not a right triangle, and $\angle C$ is not a right angle.

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Example Question #172 : Triangles

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$\bigtriangleup ABC$ is a right triangle , where $\angle A$ is a right angle, and $\overline{AE}$ is a height of the triangle. What is the measurement of $\angle ABC$ ?

(1) $\angle CAE=30^{\circ}$

(2) $\angle EAB=60^{\circ}$

Possible Answers:

Both statements taken together are sufficient

Each statement alone is sufficient

Statement 2 alone is sufficient

Statements 1 and 2 taken together are insufficient

Statement 1 alone is sufficient

Correct answer:

Each statement alone is sufficient

Explanation:

Since we are already told that triangle ABC is a right triangle, we just need to find information about other angles or other sides.

Statement 1 allows us to calculate $\angle ACE$ , simply by using the sum of the angles of a triangle, since we know AEC is also a right triangle because AE is the height.

Statement 2 is also sufficient because it allows us to know angle $\angle ACB$ . Indeed, in a right triangle, the height divides the triangles in two triangles with similar properties. Therefore angle $\angle ACB$ is the same as $\angle EAB$ .

Therefore, each statement alone is sufficient.

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Example Question #3 : Dsq: Calculating An Angle In A Right Triangle

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Given: $\bigtriangleup ABC$ is a right triangle with height $\overline{AD}$ and $\angle A$ is a right angle.

What is the size of $\angle {ABC}$ ?

(1) $\overline{AD}=\overline{DC}$

(2) $\overline{AC}=4$

Possible Answers:

Statement 1 alone is sufficient

Statements 1 and 2 taken together are not sufficient

Both statements together are sufficient

Statement 2 alone is sufficient

Each statement alone is sufficient

Correct answer:

Statement 1 alone is sufficient

Explanation:

In order to find the angles of right triangle ABC, we would need to find the length of the sides and maybe found that the triangle is isoceles, or is a special triangle with angles 30-60-90.

Statement one tells us that the height is equal to half the hypothenuse of the triangle. From that we can see that the triangle is isoceles. Indeed, an isoceles right triangle will always have its height equal to half the length of the hypothenuse. Therefore we will know that both angles are 45 degrees. Statement 1 alone is sufficient.

Statement 2 alone is insufficient because we don't know anything about the other sides of the triangle. Therefore it doesn't help us.

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Example Question #4 : Dsq: Calculating An Angle In A Right Triangle

You are given two right triangles: $\triangle ABC$ with right angle , and $\triangle XYZ$ with right angle .

True or false: $\triangle ABC \sim \triangle XYZ$

Statement 1: $\angle A \cong \angle Y$

Statement 2: $\angle B \cong \angle X$

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.

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.

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:

For $\triangle ABC \sim \triangle XYZ$ , it is necessary that corresponding angles be congruent - specifically, $m \angle A = m \angle X$ and $m \angle B = m \angle Y$ . We show that the statements together are insufficient by assuming them both to be true and examining two cases:

Case 1: $m \angle A = m \angle B = m \angle X = m \angle Y = 45^{\circ }$ .

Case 2: $m \angle A = m \angle Y = 30^{\circ }$ and $m \angle B = m \angle X= 60^{\circ }$ .

Both cases fit the main body of the problem and both statements, but in the first case, $m \angle A = m \angle X$ , and in the second case, $m \angle A \ne m \angle X$ . The statement $\triangle ABC \sim \triangle XYZ$ holds only in the first case but not in the second. (Note that in both cases, $\triangle ABC \sim \triangle YXZ$ , but this is a different statement.)

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Example Question #6 : Dsq: Calculating An Angle In A Right Triangle

Given a right triangle $\bigtriangleup ABC$ with right angle $\angle B$ , what is the measure of $\angle A$ ?

Statement 1: $\bigtriangleup ABC \sim \bigtriangleup CBA$

Statement 2: AB = BC

Possible Answers:

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

Correct answer:

EITHER STATEMENT ALONE provides sufficient information to answer the question.

Explanation:

Corresponding angles of similar triangles - including the same triangle, considered in different configurations - are congruent. It follows from Statement 1 alone that $\angle A \cong \angle C$ . The measures of the acute angles of a right triangle add up to $90^{\circ }$ , so:

$m \angle A + m \angle C =90 ^{\circ }$

$m \angle A + m \angle A =90 ^{\circ }$

$2 \cdot m \angle A =90 ^{\circ }$

$m \angle A =45 ^{\circ }$

Assume Statement 2 alone. By the 45-45-90 Theorem, since the legs of the right triangle are of equal length, the acute angles of the triangle, one of which is $\angle A$ , measures $45 ^{\circ }$ .

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Example Question #421 : Geometry

Given a right triangle $\bigtriangleup ABC$ with right angle $\angle B$ , what is the measure of $\angle A$ ?

Statement 1: An arithmetic sequence can be written that begins as follows: $m \angle A, m \angle C, 75^{\circ }$

Statement 2: $m \angle A$ is a whole number and a multiple of both 5 and 7.

Possible Answers:

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

Correct answer:

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

Explanation:

Assume Statement 1 alone, and let be the measure of $\angle A$ . The sum of the measures of the acute angles of a right triangle, $\angle A$ and $\angle C$ , is $90^{\circ }$ , so

$m \angle A + m \angle C = 90^{\circ }$

$X + m \angle C = 90^{\circ }$

$X + m \angle C -X = 90^{\circ } -X$

$m \angle C = 90^{\circ } -X$

The first two terms of the arithmetic sequence given are and 90 - X . In an arithmetic sequence, each term is obtained by adding the same number, or common difference. This is the difference of the second and first terms, or

$90 ^{\circ }- X - X = 90^{\circ } - 2X$ ,

which is added to the second term to get the third term:

$(90^{\circ } - X )+ (90^{\circ } - 2X) = 180 ^{\circ }- 3X$

The third term is $75^{\circ }$ , so

$180 ^{\circ } - 3X = 75^{\circ }$

$180 ^{\circ } - 3X - 180 ^{\circ } = 75^{\circ } - 180 ^{\circ }$

$- 3X = - 105 ^{\circ }$

$- 3X \div (-3) = - 105 ^{\circ } \div (-3)$

$X = 35 ^{\circ }$ , the measure of $\angle A$ .

Assume Statement 2 alone. $\angle B$ is the right angle of the triangle, so $\angle A$ is an acute angle; it will have measure less than $90^{\circ }$ . Its measure is a whole number less than 90 which is, by Statement 2, a multiple of 5 and 7. However, both 35 and 70 are multiples of 5 and 7, so $m \angle A$ can be either, and no information is given that eliminates either choice.

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Example Question #533 : Data Sufficiency Questions

A right triangle $\bigtriangleup ABC$ with right angle $\angle B$ ; all of its interior angles have degree measures that are whole numbers. What is the measure of $\angle A$ ?

Statement 1: $m \angle A$ is a perfect cube integer.

Statement 2: $m \angle C$ is a multiple of both 7 and 9.

Possible Answers:

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

Correct answer:

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

Explanation:

An acute angle must have measure less than $90^{\circ }$ ; both non-right angles of the triangle, $\angle A$ and $\angle C$ , must be acute, and thus have measure less than $90^{\circ }$ .

Assume Statement 1 alone. There are four perfect cubes less than 90 - 1, 8, 27, and 64 - so $\angle A$ can have any one of these four degree measures. There is no way to eliminate any one of these four.

Assume Statement 2 alone. The least common multiple of 7 and 9 is 63, so, since $m \angle C$ is a multiple of both 7 and 9, it must be a multiple of 63. The only multiple of 63 less than 90 is 63 itself, so $m \angle C = 63^{\circ }$ . The acute angles of a right angle have degree measures that total $90^{\circ }$ , so

$m \angle A + m \angle C = 90^{\circ }$

$m \angle A + 63^{\circ } = 90^{\circ }$

$m \angle A = 90^{\circ } - 63^{\circ } = 27^{\circ }$

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Example Question #9 : Dsq: Calculating An Angle In A Right Triangle

A right triangle $\bigtriangleup ABC$ with right angle $\angle B$ ; all of its interior angles have degree measures that are whole numbers. What is the measure of $\angle A$ ?

Statement 1: $m \angle A$ is a multiple of both 6 and 7.

Statement 2: $m \angle C$ is a multiple of 6 and 8.

Possible Answers:

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Correct answer:

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Explanation:

An acute angle must have measure less than $90^{\circ }$ ; both non-right angles of the triangle, $\angle A$ and $\angle C$ , must be acute.

Assume Statement 1 alone. The measure of $\angle A$ must be a multiple of 6 and 7 that is less than 90; however, there are at least two such numbers, 42 and 84. With no way to eliminate either choice, Statement 1 alone provides insufficient information.

Statement 2 alone also provides insufficient information, for similar reasons. $\angle C$ can have measure 24 or 48, for example; the measure of $\angle A$ is 90 minus the measure of $\angle C$ , so if $m \angle C$ cannot be determined definitively, neither can $m \angle A$ .

Now, assume both statements to be true. 6 and 7 have LCM 42, so any multiple of both must also be a multiple of 42. There are only two multiples of 42 less than 90 - 42 and 84.

If $m \angle A = 42^{\circ }$ , then, since the measures of the angles of the acute angles of a right triangle total $90^{\circ }$ ,

$m \angle A+ m \angle C = 90^{\circ }$

$42 ^{\circ }+ m \angle C = 90^{\circ }$

$m \angle C = 90^{\circ } - 42 ^{\circ } = 48 ^{\circ }$

48 is a multiple of both 6 and 8, so this scenario is consistent with both statements.

If $m \angle A = 84^{\circ }$ , then, since the measures of the angles of the acute angles of a right triangle total $90^{\circ }$ ,

$m \angle A+ m \angle C = 90^{\circ }$

$84^{\circ }+ m \angle C = 90^{\circ }$

$m \angle C = 90^{\circ } - 84^{\circ } = 6^{\circ }$

6 is not a multiple of 8, so this scenario is inconsistent with Statement 2.

Therefore, it can be determined that $m \angle A = 42^{\circ }$ .

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Example Question #6 : Dsq: Calculating An Angle In A Right Triangle

Is $\bigtriangleup ABC$ an acute triangle, a right triangle, or an obtuse triangle?

Statement 1: The measures of the angles of the triangle, when they are arranged in ascending order, form an arithmetic sequence.

Statement 2: $m \angle A = 30^{\circ }$

Possible Answers:

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Correct answer:

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

Explanation:

Assume Statement 1 alone. Let be the measure of the angle of second-greatest measure. Since the measures form an arithmetic sequence, the three angles measure y - d, y, y+d for some common difference . Their sum is $180^{\circ }$ , so

$(y - d) + y + (y+d) = 180^{\circ }$

$3y= 180^{\circ }$

$y= 60^{\circ }$

However, since we do not know that common difference, we cannot determine the other angle measures, or whether the triangle is acute, right, or obtuse. For example, if d = 1 , the widest of the angles measures $61^{\circ }$ ; if d = 31 , the widest angle measures $91^{\circ }$ . In the former case, the triangle is acute, having all of its angles measure less than $90^{\circ }$ ; in the latter case, the triangle is obtuse, having an angle that measures greater than $90^{\circ }$ .

Statement 2 alone provides insufficient information; a 30-30-120 triangle and a 30-60-90 triangle both fit this condition as well as the conditions of the measures of the angles of a triangle, but the former is obtuse and the latter is right.

Now assume both statements to be true. Then, since one angle measures $60^{\circ }$ by Statement 1, and a second measures $30^{\circ }$ , the third measures $\left [180 - (30+60) \right ]^{\circ } = 90^{\circ }$ . This angle is a right angle, so $\bigtriangleup ABC$ is a right triangle.

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GMAT Math : DSQ: Calculating an angle in a right triangle

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Dsq: Calculating An Angle In A Right Triangle

Example Question #2 : Dsq: Calculating An Angle In A Right Triangle

Example Question #172 : Triangles

Example Question #3 : Dsq: Calculating An Angle In A Right Triangle

Example Question #4 : Dsq: Calculating An Angle In A Right Triangle

Example Question #6 : Dsq: Calculating An Angle In A Right Triangle

Example Question #421 : Geometry

Example Question #533 : Data Sufficiency Questions

Example Question #9 : Dsq: Calculating An Angle In A Right Triangle

Example Question #6 : Dsq: Calculating An Angle In A Right Triangle

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