GMAT Math : Right Triangles

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Example Question #1 : Calculating Whether Right Triangles Are Similar

Which set of side lengths cannot be the side lengths of a right triangle?

Possible Answers:

$\dpi{100} \small 28,45,53$

$\dpi{100} \small 48,64,80$

$\dpi{100} \small 84,35,91$

$\dpi{100} \small 3,4,5$

$\dpi{100} \small 45, 55,75$

Correct answer:

$\dpi{100} \small 45, 55,75$

Explanation:

For a triangle to be a right triangle, the sides must obey the Pythagorean Theorem. Let's try our options.

3, 4, 5: You should know this is a right triangle without having to do any calculations because it is one of the special triangles that you should remember. But if you didn't, $3^{2} + 4^{2} = 25 = 5^{2}$ .

28, 45, 53: $28^{2} + 45^{2} = 784 + 2025 = 2809 = 53^{2}$

45, 55, 75: $45^{2} + 55^{2} = 2025 + 3025 = 5050 \neq 75^{2}$ . The sides don't follow the Pythagorean Theorem so this can't be a right triangle. This is our answer. Let's check the remaining two sets of sides as well.

48, 64, 80: $48^{2} + 64^{2} = 2304 + 4096 = 6400 = 80^{2}$ . These are pretty big numbers and this math might take a while. Instead of doing these calculations, we could also see if 48, 64, and 80 look like any of the special triangles we know. Let's divide the three numbers by 16. 48/16 = 3, 64/16 = 4, and 80/16 = 5. Then this is just a type of 3,4,5 triangle, which we know is a right triangle.

84, 35, 91: $84^{2} + 35^{2} = 7056 + 1225 = 8281 = 91^{2}$ . Again, these are big numbers to square. Let's divide the three numbers by their greatest common factor, 7. 84/7 = 12, 35/7 = 5, 91/7 = 13. Then this is a 5, 12, 13 triangle, which is another of our special triangles that we know is a right triangle.

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Example Question #2 : Right Triangles

Which of the following right triangles is similar to one with a height of and a base of ?

Possible Answers:

h=5,b=10

h=10,b=15

h=8,b=14

h=7,b=12

h=12,b=20

Correct answer:

h=10,b=15

Explanation:

In order for two right triangles to be similar, the ratio of their dimensions must be equal. First we can check the ratio of the height to the base for the given triangle, and then we can check each answer choice for the triangle with the same ratio:

$Given:\frac{h}{b}=\frac{6}{9}=\frac{2}{3}$

So now we can check the ratio of the height to the base for each answer option, in no particular order, and the one with the same ratio as the given triangle will be a triangle that is similar:

$Option1:\frac{h}{b}=\frac{5}{10}=\frac{1}{2}$

$Option2:\frac{h}{b}=\frac{7}{12}$

$Option3:\frac{h}{b}=\frac{8}{14}=\frac{4}{7}$

$Option4:\frac{h}{b}=\frac{12}{20}=\frac{3}{5}$

$Option5:\frac{h}{b}=\frac{10}{15}=\frac{2}{3}$

The triangle with a height of and a base of has the same ratio as the given triangle, so this one is similar.

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Example Question #3 : Right Triangles

Which of the following right triangles is similar to one with a height of and a base of ?

Possible Answers:

h=7, b=14

h=3, b=1

h=6, b=2

h=2, b=6

h=3, b=5

Correct answer:

h=2, b=6

Explanation:

In order for two right triangles to be similar, their height-to-base ratios must be equal. Given a right triangle with a height h=4 and a base b=12 , the ratio $\frac{h}{b}=\frac{4}{12}=\frac{1}{3}$ . The only answer provided with a ratio of $\frac{1}{3}$ is h=2, b=6 .

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Example Question #4 : Right Triangles

Which of the following right triangles is similar to one with a height of and a base of ?

Possible Answers:

h=6, b=18

h=10, b=4

h=3, b=12

h=2, b=12

h=7, b=35

Correct answer:

h=3, b=12

Explanation:

In order for two right triangles to be similar, their height-to-base ratios must be equal. Given a right triangle with a height h=5 and a base b=20 , the ratio $\frac{h}{b}=\frac{5}{20}=\frac{1}{4}$ . The only answer provided with a ratio of $\frac{1}{4}$ is h=3, b=12 .

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Example Question #1 : Calculating Whether Right Triangles Are Similar

Which of the following right triangles is similar to one with a height of and a base of ?

Possible Answers:

h=1, b=4

h=9, b=81 h=3, b=45

h=5, b=30

None of the above

h=6, b=48

Correct answer:

h=5, b=30

Explanation:

In order for two right triangles to be similar, their height-to-base ratios must be equal. Given a right triangle with a height of and a base of , the ratio $\frac{h}{b}=\frac{7}{42}=\frac{1}{6}$ . The only answer provided with a ratio of $\frac{1}{6}$ is h=5, b=30 .

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Example Question #6 : Right Triangles

Given two right triangles $\bigtriangleup ABC$ and $\bigtriangleup DEF$ , with right angles $\angle B, \angle E$ , what is the measure of $\angle A$ ?

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

Statement 2: $\bigtriangleup ABC \sim \bigtriangleup FED$

Possible Answers:

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.

EITHER 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:

Corresponding angles of similar triangles are congruent, so Statement 1 alone establishes that $\angle A \cong \angle D$ and $\angle C \cong \angle F$ ; similarly, Statement 2 alone establishes that $\angle A \cong \angle F$ and $\angle C \cong \angle D$ . However, neither statement alone establishes the actual measure of any of the four acute angles.

Assume both statements are true. From transitivity, it holds that $\angle A \cong \angle D \cong \angle C$ . Specifically, the two acute angles of $\bigtriangleup ABC$ , one of which is $\angle A$ , are congruent. Since $\angle B$ is right, this makes $\bigtriangleup ABC$ and isosceles right triangle, and its acute angles, including $\angle A$ , have measure $45 ^{\circ }$ .

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Example Question #7 : Right Triangles

What is the side length of a right triangle with a hypotenuse of and a side of ?

Possible Answers:

Correct answer:

Explanation:

We need to use the Pythagorean theorem:

a^2+b^2=c^2

a^2=c^2-b^2

a^2=10^2-8^2

a^2=100-64

a^2=36

a=6

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Example Question #1 : Calculating The Length Of The Side Of A Right Triangle

There is a big square that consists of four identical right triangles and a small square. If the area of the small square is 1, the area of the big square is 5, what is the length of the shortest side of the right triangles?

Possible Answers:

$\dpi{100} \small 3$

$\dpi{100} \small 4$

$\dpi{100} \small 5$

$\dpi{100} \small 2$

$\dpi{100} \small 1$

Correct answer:

$\dpi{100} \small 1$

Explanation:

The area of the big square is 5, and area of the small square is 1. Therefore, the area of the four right triangles is $\dpi{100} \small 5-1=4$ .

Since the four triangles are all exactly the same, the area of each of the right triangle is 1. We know that the longer side is 2 times the shorter side, so we can represent the shorter side as $\dpi{100} \small x$ and the longer side as $\dpi{100} \small 2x$ . Then we are able to set up an equation:

$\dpi{100} \small \frac{1}{2}\times x\times 2x=1$ .

Therefore, x, the length of the shortest side of the right triangle, is 1.

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Example Question #1 : Right Triangles

A triangle has sides of length 9, 12, and 16. Which of the following statements is true?

Possible Answers:

The triangle cannot exist.

The triangle is acute and isosceles.

The triangle is acute and scalene.

The triangle is obtuse and isosceles.

The triangle is obtuse and scalene.

Correct answer:

The triangle is obtuse and scalene.

Explanation:

This triangle can exist by the Triangle Inequality, since the sum of the lengths of its shortest two sides exceeds that of the longest side:

9 + 12 = 21 > 16

The sum of the squares of its shortest two sides is less than the square of that of its longest side:

$9^{2}+12^{2} = 81+144= 225 <256=16^{2}$

This makes the triangle obtuse.

Its sides are all of different measure, which makes the triangle scalene as well.

Obtuse and scalene is the correct choice.

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Example Question #10 : Right Triangles

Using the following right traingle, calculate the value of

(Not drawn to scale.)

Possible Answers:

$1\textup{ cm}$

$6.4\textup{ cm}$

$3\textup{ cm}$

$9\textup{ cm}$

Correct answer:

$3\textup{ cm}$

Explanation:

We can determine the length of the side by using the Pythagorean Theorem:

c^2=a^2+b^2

where c=5, a=4

Our equation is then:

5^2=x^2+4^2

x^2=25-16=9

x=3

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GMAT Math : Right Triangles

Study concepts, example questions & explanations for GMAT Math

All GMAT Math Resources

Example Questions

Example Question #1 : Calculating Whether Right Triangles Are Similar

Example Question #2 : Right Triangles

Example Question #3 : Right Triangles

Example Question #4 : Right Triangles

Example Question #1 : Calculating Whether Right Triangles Are Similar

Example Question #6 : Right Triangles

Example Question #7 : Right Triangles

Example Question #1 : Calculating The Length Of The Side Of A Right Triangle

Example Question #1 : Right Triangles

Example Question #10 : Right Triangles

All GMAT Math Resources

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