ACT Math : Quadrilaterals

Study concepts, example questions & explanations for ACT Math

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Example Questions

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

Find the side of a square if the area is .

Possible Answers:

Correct answer:

Explanation:

The area of a square is:

Substitute the area and solve for the side.

The quantity inside the square root may not be factorized in attempt to eliminate the square root!

The side length of the square is:

Example Question #4 : How To Find The Length Of The Side Of A Quadrilateral

Q9

Find the perimeter of the rhombus above. 

Possible Answers:

Correct answer:

Explanation:

By definition, a rhombus is a quadrilateral with four equal sides whose angles do not all equal 90 degrees. To find the perimeter, we must find the values of x and y. In order to do so, we must set up a system of equations where we set two sides equal to each other. Any two sides can be used to create these systems.

Here is one example:

Eq. 1

Eq. 2

 

Now we plug  into the first equation to find the value of :

Plugging these values into any of the three equations will give us the length of one side equaling 11.

Since there are four sides, .

Example Question #1 : How To Find An Angle In A Quadrilateral

Q6

 bisects . If  then, in degrees, what is the value of ?

Possible Answers:

Correct answer:

Explanation:

A rectangle has two sets of parallel sides with all angles equaling 90 degrees. 

Since  bisects  into two equal parts, this creates an isosceles triangle .

Therefore . The sum of the angles in a triangle is 180 degrees.

Therefore 

Example Question #2 : How To Find An Angle In A Quadrilateral

Q8

The rhombus above is bisected by two diagonals.

If  and  then, in degrees, what is the value of the ?

Note: The shape above may not be drawn to scale. 

Possible Answers:

Correct answer:

Explanation:

A rhombus is a quadrilateral with two sets of parallel sides as well as equal opposite angles. Since the lines drawn inside the rhombus are diagonals,  and  are each bisected into two equal angles.

Therefore,  , which creates a triangle in the upper right quadrant of the kite. The sum of angles in a triangle is 180 degreees.

Thus,

 

Since  is only half of ,

Example Question #1 : How To Find An Angle In A Quadrilateral

Q10

If  and , then, in degrees, what is the value of ?

 

Note: The figure may not be drawn to scale. 

Possible Answers:

Correct answer:

Explanation:

In a rhombus, opposite angles are equal to each other. Therefore we can set  and  equal to one another and solve for :

Therefore,

A rhombus, like any other quadrilateral, has a sum of angles of 360 degrees.

 

Example Question #4 : How To Find An Angle In A Quadrilateral

The interior angles of a quadrilateral are , and . What is the measure of the smallest angle of the quadrilateral?

Possible Answers:

Correct answer:

Explanation:

In order to solve this problem we need the following key piece of knowledge: the interior angles of a quadrilateral add up to 360 degrees. Now, we can write the following equation:

When we combine like terms, we get the following:

We will need to subtract 71 from both sides of the equation:

Now, we will divide both sides of the equation by 17.

We now have a value for the x-variable; however, the problem is not finished. The question asks for the measure of the smallest angle. We know that the smallest angle will be one of the following: 

 or 

In order to find out, we will substitute 17 degrees for the x-variable.

Because 51 degrees is less than 71 degrees, the measure of the smallest angle is the following:

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

A homeowner wants to set up a rectangular enclosure for his dog. The plot of land that the enclosure will enclose measures  by . What is the length in feet of chain link fence the owner will need to create a fence around the enclosure?

Possible Answers:

Correct answer:

Explanation:

To answer this question, we must find the perimeter of the fence the homeowner is wanting to create.

To find the perimeter of a rectangle, we multiply the length by two, multiply the width by two, and add these two numbers together. The equation can be represented as this:

We must then plug in our values of  and  given to us for the length and width.

So for this data:

Therefore, the amount of fencing needed to fully surround the dog's enclosure is .

Example Question #1 : How To Find An Angle In A Rhombus

The two acute angles in a rhombus add up to . What is the measure of one of the obtuse angles in the rhombus?

Possible Answers:

Correct answer:

Explanation:

The key here is to know that a rhombus has two pairs of congruent angles. In other words, the two acute angles of a rhombus are equal and the two obtuse angles are equal. 

In this problem, since the two acute angles add up to  and they must both be the same amount, each of the acute angles must be .

It is also important to know that the four angles of a rhombus add up to . If the two acute angles add up to , then that means that the two obtuse angles must add up to , or .

Finally, because the obtuse angles add up to  and they must be congruent, each of the obtuse angles must be .

Example Question #2 : How To Find An Angle In A Rhombus

A rhombus has two interior angles each with a measurement of . Find the measurement for one of the two remaining angles. 

Possible Answers:

 

Correct answer:

Explanation:

First, consider that the sum total of the four interior angles in any rhombus must equal . Furthermore, a rhombus must have two sets of equivalent opposite interior angles, and a rhombus must have two sets of adjacent interior angles. The adjacent interior angles must be supplementary—meaning they have a sum total of 

One way to approach this problem is to realize that each of the remaining two angles must have the same measurement, and that each will be supplementary angles with .  Find the difference between  and  to find the solution. 

The correct answer is: 

Example Question #3 : How To Find An Angle In A Rhombus

A rhombus has an interior angle with a measurement of . Find the measurement for one of the angles that are adjacent to the angle that has a measurement of .

Possible Answers:

Correct answer:

Explanation:

A rhombus must have two sets of equivalent opposite interior angles, and a rhombus must have two sets of adjacent interior angles. The adjacent interior angles must be supplementary—meaning they have a sum total of .

If a rhombus has an interior angle that has a measurement of , the adjacent angle must equal: 


 

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