High School Math : Parallelograms

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Parallelograms

A parallelogram, with dimensions in cm, is shown below. Act1

What is the perimeter of the parallelogram, in cm?

Possible Answers:

\(\displaystyle 60\)

\(\displaystyle 52\)

\(\displaystyle 64+12\sqrt{3}\)

\(\displaystyle 76\)

\(\displaystyle 80\)

Correct answer:

\(\displaystyle 64+12\sqrt{3}\)

Explanation:

The triangle on the left side of the figure has a \(\displaystyle 30^{\circ}\) and a \(\displaystyle 90^{\circ}\) angle. Since all of the angles of a triangle must add up to \(\displaystyle 180^{\circ}\), we can find the angle measure of the third angle:

\(\displaystyle 30+90=120\)

\(\displaystyle 180-120=60^{\circ}\)

Our third angle is \(\displaystyle 60^{\circ}\) and we have a \(\displaystyle 30-60-90\) triangle.

A \(\displaystyle 30-60-90\) triangle has sides that are in the corresponding ratio of \(\displaystyle x-x\sqrt{3}-2x\). In this case, the side opposite our \(\displaystyle 30^{\circ}\) angle is \(\displaystyle 6\), so

\(\displaystyle x=6\)

We also now know that

\(\displaystyle x\sqrt{3}=6\sqrt{3}\)

\(\displaystyle 2x=12\)

Now we know all of our missing side lengths.  The right and left side of the parallelogram will each be \(\displaystyle 12\). The bottom and top will each be \(\displaystyle 20+6\sqrt{3}\). Let's combine them to find the perimeter:

\(\displaystyle Perimeter=2w+2l\)

\(\displaystyle 2\cdot (12)+2\cdot (20+6\sqrt{3})\)

\(\displaystyle 24+40+12\sqrt{3}\)

\(\displaystyle 64+12\sqrt{3}\)

 

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

Find the perimeter of the following parallelogram:

Screen_shot_2014-02-27_at_6.43.30_pm

Possible Answers:

\(\displaystyle 16m\)

\(\displaystyle 72m\)

\(\displaystyle 30m\)

\(\displaystyle 24m\)

\(\displaystyle 40m\)

Correct answer:

\(\displaystyle 40m\)

Explanation:

The formula for the perimeter of a trapezoid is:

\(\displaystyle P=b_1+b_2+e_1+e_2\),

where \(\displaystyle b\) is the length of the base and \(\displaystyle e\) is the length of the edge.

Opposite sides of a parallelogram have the same length. Therefore, both edges are \(\displaystyle 8m\) and both bases are \(\displaystyle 12m\).

Plugging in our values, we get:

\(\displaystyle P=12m+12m+8m+8m=40m\)

Example Question #1 : Parallelograms

Find the perimeter of the following parallelogram:

Screen_shot_2014-03-01_at_9.26.41_pm

Possible Answers:

\(\displaystyle 25m\)

\(\displaystyle 60m\)

\(\displaystyle 40m\)

\(\displaystyle 50m\)

\(\displaystyle 75m\)

Correct answer:

\(\displaystyle 50m\)

Explanation:

The formula for the perimeter of a parallelogram is:

\(\displaystyle P = 2(s_{long}) + 2(s_{short})\)

where \(\displaystyle s_{long}\) is the length of the longer side and \(\displaystyle s_{short}\) is the length of the shorter side.

 

Plugging in our values, we get:

\(\displaystyle P = 2(16m) + 2(9m) = 50m\)

Example Question #3 : Parallelograms

Find the perimeter of the following parallelogram:

18

Possible Answers:

\(\displaystyle 34 + 8\sqrt{2}\ m\)

\(\displaystyle 38 + 8\sqrt{2}\ m\)

\(\displaystyle 40 + 8\sqrt{2}\ m\)

\(\displaystyle 32 + 8\sqrt{2}\ m\)

\(\displaystyle 36 + 8\sqrt{2}\ m\)

Correct answer:

\(\displaystyle 38 + 8\sqrt{2}\ m\)

Explanation:

The formula for the perimeter of a parallelogram is

\(\displaystyle P = 2(side)+2(base)\).

Plugging in our values, we get:

\(\displaystyle P = 2(4\sqrt{2}\ m)+2(19\ m)\)

\(\displaystyle P = 38 + 8\sqrt{2}\ m\)

Example Question #1 : Parallelograms

ABCD is a parallelogram. BD = 5. The angles of triangle ABD are all equal. What is the perimeter of the parallelogram?

Figure_1

Possible Answers:

\(\displaystyle 15\sqrt{3}\)

\(\displaystyle 10\sqrt{3}\)

\(\displaystyle 11\sqrt{2}\)

\(\displaystyle 15\)

\(\displaystyle 20\)

Correct answer:

\(\displaystyle 20\)

Explanation:

If all of the angles in triangle ABD are equal and line BD divides the parallelogram, then all angles in triangle BDC must be equal as well.

We now have two equilateral triangles, so all sides of the triangles will be equal.

All sides therefore equal 5.

5+5+5+5 = 20

Example Question #321 : Geometry

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

Screen_shot_2013-07-15_at_9.42.14_pm

Possible Answers:

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

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

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

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

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

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 : Parallelograms

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

 

Possible Answers:

\(\displaystyle 50\)

\(\displaystyle 56\)

\(\displaystyle 15\)

\(\displaystyle 28\)

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 #3 : Parallelograms

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

Possible Answers:

\(\displaystyle 69\)

\(\displaystyle 96\)

\(\displaystyle 84\)

\(\displaystyle 48\)

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:

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

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

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

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