ACT Math : Plane Geometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #12 : How To Find An Angle In A Parallelogram

Parallelogram_8

 is a parallelogram. Find .

Possible Answers:

Correct answer:

Explanation:

In a parallelogram, consecutive angles are supplementary and opposite angles are congruent.

 

Example Question #1 : Parallelograms

In the parallellogram, what is the value of ?

Screen_shot_2013-07-15_at_9.42.14_pm

Possible Answers:

Correct answer:

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 Length Of The Side Of A Parallelogram

Parallelogram_2

In parallelogram  and . Find .

Possible Answers:

There is insufficient information to solve the problem.

Correct answer:

Explanation:

In a parallelogram, opposite sides are congruent. Thus,

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

Parallelogram_2

In parallelogram  and . Find .

Possible Answers:

There is insufficient information to solve the problem.

Correct answer:

Explanation:

In a parallelogram, opposite sides are congruent.

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

Parallelogram_9

Parallelogram  has an area of . If , find .

Possible Answers:

There is insufficient information to solve the problem.

Correct answer:

Explanation:

The area of a parallelogram is given by:

In this problem, the height is given as  and the area is . Both  and  are bases.

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

Parallelogram_10

 is a parallelogram. Find .

Possible Answers:

There is insufficient information to solve the problem.

Correct answer:

Explanation:

 is the hypotenuse of the right triangle formed when we draw the height of the parallelogram. Because it is a right triangle, we can use SOH CAH TOA to solve for . With respect to , we know the opposite side of the triangle and we are looking for the hypotenuse. Thus, we can use the sine function to solve for .

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

Find the length of the base of a parallelogram with a height of  and an area of .

Possible Answers:

Correct answer:

Explanation:

The formula for the area of a parallelogram is:

By plugging in the given values, we get:

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

Parallelogram_11

 is a parallelogram with an area of . Find .

Possible Answers:

There is insufficient information to solve the problem.

Correct answer:

Explanation:

In order to find , we must first find . The formula for the area of a parallelogram is:

We are given  as the area and  as the base.

Now, we can use trigonometry to solve for . With respect to , we know the opposite side of the right triangle and we are looking for the hypotenuse. Thus, we can use the sine function.

Example Question #91 : Quadrilaterals

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

What is the perimeter of the parallelogram, in cm?

Possible Answers:

Correct answer:

Explanation:

The triangle on the left side of the figure has a and a  angle. Since all of the angles of a triangle must add up to , we can find the angle measure of the third angle:

Our third angle is and we have a triangle.

A triangle has sides that are in the corresponding ratio of . In this case, the side opposite our angle is , so

We also now know that

Now we know all of our missing side lengths.  The right and left side of the parallelogram will each be . The bottom and top will each be . Let's combine them to find the perimeter:

 

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

Parallelogram2

Note: Figure NOT drawn to scale.

Give the perimeter of Parallelogram  in the above diagram.

Possible Answers:

Correct answer:

Explanation:

By the 30-60-90 Theorem, the length of the short leg of  is the length of the long leg divided by , so 

Its hypotenuse has twice the length of the short leg, so 

The perimeter of the parallelogram is

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