High School Math : Geometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #11 : Parallelograms

In the parallellogram, what is the value of \(\displaystyle x\)?

Screen_shot_2013-07-15_at_9.42.14_pm

Possible Answers:

\(\displaystyle 135^{\circ}\)

\(\displaystyle 145^{\circ}\)

\(\displaystyle 120^{\circ}\)

\(\displaystyle 110^{\circ}\)

\(\displaystyle 130^{\circ}\)

Correct answer:

\(\displaystyle 130^{\circ}\)

Explanation:

Opposite angles are equal, and adjacent angles must sum to 180.

Therefore, we can set up an equation to solve for z:

(z – 15) + 2z = 180

3z - 15 = 180

3z = 195

z = 65

Now solve for x:

2= x = 130°

Example Question #1 : How To Find The Area Of A Parallelogram

What is the area of a parallelogram with a base of \(\displaystyle 8\) and a height of \(\displaystyle 7\)?

 

Possible Answers:

\(\displaystyle 28\)

\(\displaystyle 56\)

\(\displaystyle 15\)

\(\displaystyle 50\)

Correct answer:

\(\displaystyle 56\)

Explanation:

To solve this question you must know the formula for the area of a parallelogram.

In this equation, \(\displaystyle B\) is the length of the base and \(\displaystyle H\) is the length of the height. We can plug in the side length for both base and height, as given in the question.

\(\displaystyle A=8*7\)

\(\displaystyle A=56\)

 

Example Question #2 : How To Find The Area Of A Parallelogram

What is the area of a parallelogram with a base of \(\displaystyle 12\) and a height of \(\displaystyle 8\)?

Possible Answers:

\(\displaystyle 48\)

\(\displaystyle 69\)

\(\displaystyle 96\)

\(\displaystyle 84\)

Correct answer:

\(\displaystyle 96\)

Explanation:

To solve this question you must know the formula for the area of a parallelogram.

The formula is 

So we can plug in the side length for both base and height to yield \(\displaystyle A=12*8\)

Perform the multiplication to arrive at the answer of \(\displaystyle A=96\).

Example Question #3 : Parallelograms

Find the area of the following parallelogram:

Screen_shot_2014-02-27_at_6.43.30_pm

Possible Answers:

\(\displaystyle 96m^2\)

\(\displaystyle 48\sqrt{3}m^2\)

\(\displaystyle 48m^2\)

Cannot be determined from the given information.

\(\displaystyle 96\sqrt{3}m^2\)

Correct answer:

\(\displaystyle 48\sqrt{3}m^2\)

Explanation:

The formula for the area of a parallelogram is:

\(\displaystyle A=(b)(h)\),

where \(\displaystyle b\) is the length of the base and \(\displaystyle h\) is the length of the height.

 

In order to the find the height of the parallelogram, use the formula for a \(\displaystyle 30-60-90\) triangle:

\(\displaystyle a-a\sqrt{3}-2a\), where \(\displaystyle a\) is the side opposite the \(\displaystyle \measuredangle30\).

The left side of the parallelogram forms the following \(\displaystyle 30-60-90\) triangle:

\(\displaystyle 4m-4\sqrt{3}m-8m\), where \(\displaystyle 4\sqrt{3}m\) is the length of the height.

 

Plugging in our values, we get:

\(\displaystyle A=(12m)(4\sqrt{3}m)=48\sqrt{3}m^2\)

Example Question #182 : Geometry

Find the area of the following parallelogram:

Screen_shot_2014-03-01_at_9.26.41_pm

Possible Answers:

\(\displaystyle 144\sqrt{7}m^2\)

\(\displaystyle 54\sqrt{7}m^2\)

\(\displaystyle 36\sqrt{7}m^2\)

\(\displaystyle 45\sqrt{7}m^2\)

\(\displaystyle 72\sqrt{7}m^2\)

Correct answer:

\(\displaystyle 45\sqrt{7}m^2\)

Explanation:

Use the Pythagorean Theorem to determine the length of the diagonal:

\(\displaystyle A^2 + B^2 = C^2\)

\(\displaystyle (9m)^2 + B^2 = (16m^2)\)

\(\displaystyle B^2 = 175m^2\)

\(\displaystyle B = 5 \sqrt{7}m\)

 

The area of the parallelogram is twice the area of the right triangles:

\(\displaystyle A_{Triangle} = \frac{1}{2} (b)(h)\)

\(\displaystyle A_{Triangle} = \frac{1}{2} (9m)(5m\sqrt{7}) = \frac{45m^2\sqrt{7}}{2}\)

\(\displaystyle A_{Parallelogram} = 2 (A_{Triangle}) = 2\left(\frac{45m^2\sqrt{7}}{2}\right)=45m^2\sqrt{7}\)

Example Question #181 : Geometry

Find the area of the following parallelogram:

18

Possible Answers:

\(\displaystyle 800\ m^2\)

\(\displaystyle 770\ m^2\)

 

 

\(\displaystyle 780\ m^2\)

\(\displaystyle 790\ m^2\)

\(\displaystyle 760\ m^2\)

Correct answer:

\(\displaystyle 760\ m^2\)

Explanation:

The formula for the area of a parallelogram is

\(\displaystyle A = (base)(height)\).

Use the formula for a \(\displaystyle 45-45-90\) triangle to find the length of the height:

\(\displaystyle a-a-a\sqrt{2}\)

\(\displaystyle 4\ m-4\ m-4\sqrt{2}\ m\)

Plugging in our values, we get:

\(\displaystyle A = (19\ m)(4\ m)\)

\(\displaystyle A = 760\ m^2\)

Example Question #1 : How To Find If Rectangles Are Similar

Two rectangles are similar. The perimeter of the first rectangle is 36. The perimeter of the second is 12. If the base length of the second rectangle is 4, what is the height of the first rectangle?

Possible Answers:

10

8

4

6

2

Correct answer:

6

Explanation:

Solve for the height of the second rectangle.

Perimeter = 2B + 2H

12 = 2(4) + 2H

12 = 8 + 2H

4 = 2H

H = 2

If they are similar, then the base and height are proportionally equal.

B1/H1 = B2/H2

4/2 = B2/H2

2 = B2/H2

B2 = 2H2

Use perimeter equation then solve for H:

Perimeter = 2B + 2H

36 = 2 B2 + 2 H2

36 = 2 (2H2) + 2 H2

36 = 4H2 + 2 H2

36 = 6H2

H2 = 6

Example Question #1 : How To Find The Perimeter Of A Rectangle

A rectangle has a width of 2x. If the length is five more than 150% of the width, what is the perimeter of the rectangle?

Possible Answers:

6x2 + 5

6x2 + 10x

5x + 5

5x + 10

10(x + 1)

Correct answer:

10(x + 1)

Explanation:

Given that w = 2x and l = 1.5w + 5, a substitution will show that l = 1.5(2x) + 5 = 3x + 5.  

P = 2w + 2l = 2(2x) + 2(3x + 5) = 4x + 6x + 10 = 10x + 10 = 10(x + 1)

Example Question #1 : How To Find The Perimeter Of A Rectangle

What is the perimeter of the below rectangle in simplest radical form?

 

                                     Act_math_159_15

Possible Answers:

7√27

5√3

10√3

4√3 + 2√27

Correct answer:

10√3

Explanation:

The perimeter of a figure is the sum of the lengths of all of its sides. The perimeter of this figure is √27 + 2√3 + √27 + 2√3. But, √27 = √9√3 = 3√3 . Now all of the sides have the same number underneath of the radical symbol (i.e. the same radicand) and so the coefficients of each radical can be added together. The result is that the perimeter is equal to 10√3.

 

 

Example Question #1 : How To Find The Perimeter Of A Rectangle

A rectangle has an area of 56 square feet, and a width of 4 feet. What is the perimeter, in feet, of the rectangle?

Possible Answers:
28
120
36
14
30
Correct answer: 36
Explanation:

Divide the area of the rectangle by the width in order to find the length of 14 feet. The perimeter is the sum of the side lengths, which in this case is 14 feet + 4 feet +14 feet + 4 feet, or 36 feet.

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