PSAT Math : Triangles

Study concepts, example questions & explanations for PSAT Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #1 : Right Triangles

Triangles

Note: Figure NOT drawn to scale.

Refer to the above figure. Given that \(\displaystyle \Delta ABC \sim \Delta DE F\), give the area of \(\displaystyle \Delta DE F\).

Possible Answers:

The correct answer is not among the other responses.

\(\displaystyle 243.75\)

\(\displaystyle 1,828.125\)

\(\displaystyle 225\)

\(\displaystyle 1,687.5\)

Correct answer:

\(\displaystyle 1,687.5\)

Explanation:

By the Pythagorean Theorem, 

\(\displaystyle BC = \sqrt{(AC)^{2} - (AB)^{2}}\)

\(\displaystyle = \sqrt{13^{2}- 5^{2}}\)

\(\displaystyle = \sqrt{169- 25}\)

\(\displaystyle = \sqrt{144}\)

\(\displaystyle = 12\)

 

The similarity ratio of \(\displaystyle \Delta DE F\) to \(\displaystyle \Delta ABC\) is 

\(\displaystyle \frac{EF}{BC} = \frac{90}{12} = 7.5\)

 

This can be used to find \(\displaystyle DE\) : 

\(\displaystyle \frac{DE}{AB} = 7.5\)

\(\displaystyle \frac{DE}{5} = 7.5\)

\(\displaystyle DE = 5 \cdot 7.5 = 37.5\)

 

The area of \(\displaystyle \Delta DE F\) is therefore 

\(\displaystyle \frac{1}{2} \cdot DE \cdot EF = \frac{1}{2} \cdot 37.5 \cdot 90 =1,687.5\)

Example Question #22 : Triangles

Triangles

Note: Figures NOT drawn to scale.

Refer to the above figure. Given that \(\displaystyle \Delta ABC \sim \Delta DE F\) , evaluate \(\displaystyle DE\).

Possible Answers:

\(\displaystyle 42\)

\(\displaystyle 52 \frac{1}{2}\)

\(\displaystyle 62\frac{1}{2}\)

\(\displaystyle 35\)

\(\displaystyle 56\)

Correct answer:

\(\displaystyle 56\)

Explanation:

By the Pythagorean Theorem, since \(\displaystyle \overline{AC}\)  is the hypotenuse of a right triangle with legs 6 and 8, its measure is 

\(\displaystyle AC = \sqrt{6^{2} + 8 ^{2}} = \sqrt{36 + 64 } = \sqrt{100} = 10\).

The similarity ratio of \(\displaystyle \Delta DE F\) to \(\displaystyle \Delta ABC\) is

\(\displaystyle \frac{DF}{AC} = \frac{70}{10} = 7\).

Likewise, 

\(\displaystyle \frac{DE}{AB} = 7\)

\(\displaystyle \frac{DE}{8} = 7\)

\(\displaystyle DE = 56\)

Example Question #72 : Right Triangles

A right triangle has one side equal to 5 and its hypotenuse equal to 14. Its third side is equal to:

Possible Answers:

171

12

9

14.87

13.07

Correct answer:

13.07

Explanation:

The Pythagorean Theorem gives us a2 + b2 = c2 for a right triangle, where c is the hypotenuse and a and b are the smaller sides. Here a is equal to 5 and c is equal to 14, so b2 = 142 – 52 = 171. Therefore b is equal to the square root of 171 or approximately 13.07.

Example Question #73 : Right Triangles

Which of the following could NOT be the lengths of the sides of a right triangle?

Possible Answers:

14, 48, 50

5, 7, 10

5, 12, 13

8, 15, 17

12, 16, 20

Correct answer:

5, 7, 10

Explanation:

We use the Pythagorean Theorem and we calculate that 25 + 49 is not equal to 100.
All of the other answer choices observe the theorem a2 + b2 = c2

Example Question #2 : How To Find The Length Of The Side Of A Right Triangle

Which set of sides could make a right triangle?

Possible Answers:

6, 7, 8

9, 12, 15

4, 6, 9

10, 12, 16

Correct answer:

9, 12, 15

Explanation:

By virtue of the Pythagorean Theorem, in a right triangle the sum of the squares of the smaller two sides equals the square of the largest side. Only 9, 12, and 15 fit this rule.

Example Question #1 : How To Find The Length Of The Side Of A Right Triangle

A right triangle with a base of 12 and hypotenuse of 15 is shown below. Find x.

Screen_shot_2013-03-18_at_10.29.39_pm

Possible Answers:

4

5.5

5

4.5

3.5

Correct answer:

4

Explanation:

Using the Pythagorean Theorem, the height of the right triangle is found to be = √(〖15〗–〖12〗2) = 9, so x=9 – 5=4

Example Question #102 : Triangles

A right triangle has sides of 36 and 39(hypotenuse).  Find the length of the third side

Possible Answers:

12 √6

33√2

42

15

33

Correct answer:

15

Explanation:

use the pythagorean theorem:

a2 + b2 = c2  ; a and b are sides, c is the hypotenuse

a2 + 1296 = 1521

a2 = 225

a = 15

Example Question #2 : How To Find The Length Of The Side Of A Right Triangle

Bob the Helicopter is at 30,000 ft. above sea level, and as viewed on a map his airport is 40,000 ft. away. If Bob travels in a straight line to his airport at 250 feet per second, how many minutes will it take him to arrive?

Possible Answers:

4 hours and 0 minutes

2 hours and 30 minutes

1 hour and 45 minutes

3 minutes and 50 seconds

3 minutes and 20 seconds

Correct answer:

3 minutes and 20 seconds

Explanation:

Draw a right triangle with a height of 30,000 ft. and a base of 40,000 ft. The hypotenuse, or distance travelled, is then 50,000ft using the Pythagorean Theorem. Then dividing distance by speed will give us time, which is 200 seconds, or 3 minutes and 20 seconds.

Example Question #3 : How To Find The Length Of The Side Of A Right Triangle

A right triangle has two sides, 9 and x, and a hypotenuse of 15. What is x?

Possible Answers:

14

10

11

12

13

Correct answer:

12

Explanation:

We can use the Pythagorean Theorem to solve for x.

92 + x2 = 152

81 + x2 = 225

x2 = 144

x = 12

Example Question #5 : How To Find The Length Of The Side Of A Right Triangle

The area of a right traingle is 42. One of the legs has a length of 12. What is the length of the other leg?

Possible Answers:

6\(\displaystyle 6\)

5\(\displaystyle 5\)

11\(\displaystyle 11\)

9\(\displaystyle 9\)

7\(\displaystyle 7\)

Correct answer:

7\(\displaystyle 7\)

Explanation:

Area= \frac{1}{2}\times base\times height\(\displaystyle Area= \frac{1}{2}\times base\times height\)

42=\frac{1}{2}\times base\times 12\(\displaystyle 42=\frac{1}{2}\times base\times 12\)

42=6\times base\(\displaystyle 42=6\times base\)

base=7\(\displaystyle base=7\)

Learning Tools by Varsity Tutors