ACT Math : Geometry

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #41 : Geometry

If the perimeter of a regular hexagon is \(\displaystyle 112.8\), what is the length of a side of that regular hexagon?

Possible Answers:

\(\displaystyle 19.6\)

\(\displaystyle 19.8\)

\(\displaystyle 18.8\)

\(\displaystyle 18.6\)

Correct answer:

\(\displaystyle 18.8\)

Explanation:

Use the formula for perimeter to solve for the length of a side of the regular hexagon:

\(\displaystyle P=6s\)

Where \(\displaystyle P\) is perimeter and \(\displaystyle s\) is the length of a side.

In this case:

\(\displaystyle 112.8=6s\)

\(\displaystyle s=\frac{112.8}{6}=18.8\)

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

Find the length of one side for a regular hexon with a perimeter of \(\displaystyle 85.8\).

Possible Answers:

\(\displaystyle 15.2\)

\(\displaystyle 14.3\)

\(\displaystyle 12.4\)

\(\displaystyle 13.6\)

Correct answer:

\(\displaystyle 14.3\)

Explanation:

Use the formula for perimeter to solve for the side length:

\(\displaystyle P=6s\)

\(\displaystyle 85.8=6s\)

\(\displaystyle s=14.3\)

Example Question #1 : Hexagons

Find the length of one side for a regular hexagon with a perimeter of \(\displaystyle 114\).

Possible Answers:

\(\displaystyle 18\)

\(\displaystyle 18.5\)

\(\displaystyle 16\)

\(\displaystyle 19\)

Correct answer:

\(\displaystyle 19\)

Explanation:

Use the formula for perimeter to solve for the side length:

\(\displaystyle P=6s\)

\(\displaystyle 114=6s\)

\(\displaystyle s=19\)

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

What is the maximum length of each side for a regular hexago with a perimeter of \(\displaystyle 54\)?

Possible Answers:

\(\displaystyle 9\)

8.8

\(\displaystyle 7.6\)

\(\displaystyle 9.4\)

Correct answer:

\(\displaystyle 9\)

Explanation:

Use the formula for perimeter to solve for the side length:

\(\displaystyle P=6s\)

\(\displaystyle 54=6s\)

\(\displaystyle s=9\)

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

What is the side of a Hexagon whose area is \(\displaystyle 216\sqrt3\textup{ m}^2\)?

Possible Answers:

\(\displaystyle s = \sqrt{72}\textup{m}\)

\(\displaystyle s = 12\textup{m}^2\)

\(\displaystyle s = 12\textup{m}\)

\(\displaystyle s = \sqrt{108}\textup{m}\)

\(\displaystyle s = 12\sqrt{3}\textup{m}\)

Correct answer:

\(\displaystyle s = 12\textup{m}\)

Explanation:

To find the side of a hexagon given the area, set the area formula equal to the given area and solve for the side.
\(\displaystyle 216\sqrt{3}=\frac{3}{2}\sqrt{3}*a^2 \newline \newline 432\sqrt3 = 3\sqrt{3}*a^2 \newline \newline 432 = 3*a^2 \newline 144 = a^2 \newline 12 = a\)

Example Question #41 : Plane Geometry

The sum of all the angles inside of a regular hexagon is \(\displaystyle 720^{\circ}\). Determine the value of one angle. 

Possible Answers:

\(\displaystyle 220^{\circ}\)

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

\(\displaystyle 160^{\circ}\)

\(\displaystyle 140^{\circ}\)

\(\displaystyle 180^{\circ}\)

Correct answer:

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

Explanation:

In a regular hexagon, all of the sides are the same length, and all of the angles are equivalent. The problem tells us that all of the angles inside the hexagon sum to \(\displaystyle 720^{\circ}\). To find the value of one angle, we must divide \(\displaystyle 720^{\circ}\) by \(\displaystyle 6\), since there are \(\displaystyle 6\) angles inside of a hexagon. 

\(\displaystyle \frac{720 ^{\circ}}{6}=120^{\circ}\)

Example Question #11 : Hexagons

Hexex11

All of the angles marked are exterior angles.

What is the value of \(\displaystyle a\) in degrees? Round to the nearest hundredth.

Possible Answers:

\(\displaystyle 32.73^{\circ}\)

\(\displaystyle 25.20^{\circ}\)

\(\displaystyle 40.00^{\circ}\)

\(\displaystyle 31.14^{\circ}\)

\(\displaystyle 65.45^{\circ}\)

Correct answer:

\(\displaystyle 32.73^{\circ}\)

Explanation:

There are two key things for a question like this. The first is to know that a polygon has a total degree measure of:

\(\displaystyle 180*(s-2)\), where \(\displaystyle s\) is the number of sides.

Therefore, a hexagon like this one has:

\(\displaystyle 180*4=720^{\circ}\).

Next, you should remember that all of the exterior angles listed are supplementary to their correlative interior angles. This lets you draw the following figure:

Hexex12

Now, you just have to manage your algebra well. You must sum up all of the interior angles and set them equal to \(\displaystyle 720\). Since there are \(\displaystyle 6\) angles, you know that the numeric portion will be \(\displaystyle 180*6\) or \(\displaystyle 1080\). Thus, you can write:

\(\displaystyle 1080-a-2a-a-3a-a-3a=720\)

Simplify and solve for \(\displaystyle a\):

\(\displaystyle 1080-11a=720\)

\(\displaystyle -11a=-360\)

\(\displaystyle a=\frac{360}{11}\)

This is \(\displaystyle 32.72727272727272...\) or \(\displaystyle 32.73^{\circ}\).

Example Question #43 : Geometry

Hexex21

The figure above is a hexagon.  All of the angles listed (except the interior one) are exterior angles to the hexagon's interior angles.

What is the value of \(\displaystyle x\)?

Possible Answers:

\(\displaystyle 60^{\circ}\)

\(\displaystyle 75^{\circ}\)

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

\(\displaystyle 150^{\circ}\)

\(\displaystyle 50^{\circ}\)

Correct answer:

\(\displaystyle 50^{\circ}\)

Explanation:

There are two key things for a question like this. The first is to know that a polygon has a total degree measure of:

\(\displaystyle 180*(s-2)\), where \(\displaystyle s\) is the number of sides.

Therefore, a hexagon like this one has:

\(\displaystyle 180*4=720^{\circ}\).  

Next, you should remember that all of the exterior angles listed are supplementary to their correlative interior angles.  This lets you draw the following figure: 

Hexex22

Now, you just have to manage your algebra well. You must sum up all of the interior angles and set them equal to \(\displaystyle 720\). Thus, you can write:

\(\displaystyle 140+160+150+85+135+x=720\)

Solve for \(\displaystyle x\):

\(\displaystyle 670+x=720\)

\(\displaystyle x=50^{\circ}\)

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

A hexagon is made up of 6 congruent equilateral triangles. Each equilateral triangle has a length of 8 units. What is the area in square units of the hexagon?

Possible Answers:

\(\displaystyle 64\sqrt2\)

\(\displaystyle 96\sqrt3\)

\(\displaystyle 96\sqrt2\)

\(\displaystyle 64\sqrt3\)

\(\displaystyle 16\sqrt3\)

Correct answer:

\(\displaystyle 96\sqrt3\)

Explanation:

First, let's draw out the hexagon.

Hexagon

Because the hexagon is made up of 6 equilateral triangles, to find the area of the hexagon, we will first find the area of each equilateral triangle then multiply it by 6.

Equitr

Using the Pythagorean Theorem, we find that the height of each equilateral triangle is \(\displaystyle 4\sqrt3\).

 

The area of the triangle is then

\(\displaystyle \frac{8 \times 4\sqrt3}{2}=16\sqrt3\)

 

Multiply this value by 6 to find the area of the hexagon.

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

What is the area of a regular hexagon with a side length of \(\displaystyle 6\:units\)?

Possible Answers:

\(\displaystyle 36\:units^2\)

\(\displaystyle 54\sqrt{3}\:units^2\)

\(\displaystyle 36\sqrt{2}\:units^2\)

\(\displaystyle 18\sqrt{3}\:units^2\)

\(\displaystyle 216\:units^2\)

Correct answer:

\(\displaystyle 54\sqrt{3}\:units^2\)

Explanation:

This question is asking about the area of a regular hexagon that looks like this:

Hex6

Now, you could proceed by noticing that the hexagon can be divided into little equilateral triangles:

Hexagontriangle

By use of the properties of isosceles and \(\displaystyle 30-60-90\) triangles, you could compute that the area of one of these little triangles is:

\(\displaystyle \frac{\sqrt{3}}{4}s^2\), where \(\displaystyle s\) is the side length. Since there are \(\displaystyle 6\) of these triangles, you can multiply this by \(\displaystyle 6\) to get the area of the regular hexagon:

\(\displaystyle 6*\frac{\sqrt{3}}{4}s^2=\frac{3\sqrt{3}}{2}s^2\)

It is likely easiest merely to memorize the aforementioned equation for the area of an equilateral triangle. From this, you can derive the hexagon area equation mentioned above. Using this equation and our data, we know:

\(\displaystyle Area=\frac{3\sqrt{3}}{2}*6^2=\frac{3\sqrt{3}}{2}*36=54\sqrt{3}\)

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