GRE Math : Cubes

Study concepts, example questions & explanations for GRE Math

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Example Questions

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Example Question #1 :How To Find The Length Of An Edge Of A Cube

Quantity A: The length of a side of a cube with a volume of

Quantity B: The length of a side of a cube with surface area of

Which of the following is true?

Possible Answers:

Quantity A is larger.

The two quantities are equal

Quantity B is larger.

The relationship between the two quantities cannot be determined.

Correct answer:

The two quantities are equal

Explanation:

Recall that the equation for the volume of a cube is:

Since the sides of a cube are merely squares, the surface area equation is justtimes the area of one of those squares:

So, for our two quantities:

Quantity A

Use your calculator to estimate this value (since you will not have a square root key). This is

Quantity B

First divide by:

Therefore,

因此,届e two quantities are equal.

Example Question #2 :How To Find The Length Of An Edge Of A Cube

What is the length of an edge of a cube with a surface area of?

Possible Answers:

Correct answer:

Explanation:

The surface area of a cube is made up ofsquares. Therefore, the equation is merelytimes the area of one of those squares. Since the sides of a square are equal, this is:

, whereis the length of one side of the square.

For our data, we know:

This means that:

Now, while you will not have a calculator with a square root key, you do know that。(You can always use your calculator to test values like this.) Therefore, we know that。这是一条边的长度

Example Question #3 :How To Find The Length Of An Edge Of A Cube

我f a cube has a total surface area ofsquare inches, what is the length of one edge?

Possible Answers:

There is not enough information given.

Correct answer:

Explanation:

There are 6 sides to a cube. If the total surface area is 54 square inches, then each face must have an area of 9 square inches.

Every face of a cube is a square, so if the area is 9 square inches, each edge must be 3 inches.

Example Question #1 :How To Find The Diagonal Of A Cube

The surface area of a cube is 486 units. What is the distance of its diagonal (e.g. from its front-left-bottom corner to its rear-right-top corner)?

Possible Answers:

9√(2)

81

9

None of the others

9√(3)

Correct answer:

9√(3)

Explanation:

First, we must ascertain the length of each side. Based on our initial data, we know that the 6 faces of the cube will have a surface area of 6x2。This yields the equation:

6x2= 486, which simplifies to: x2= 81; x = 9.

Therefore, each side has a length of 9. Imagine the cube is centered on the origin. This means its "front-left-bottom corner" will be at (–4.5, –4.5, 4.5) and its "rear-right-top corner" will be at (4.5, 4.5, –4.5). To find the distance between these, we use the three-dimensional distance formula:

d = √((x1– x2)2+ (y1– y2)2+ (z1– z2)2)

For our data, this will be:

√( (–4.5 – 4.5)2+ (–4.5 – 4.5)2+ (4.5 + 4.5)2) =

√( (–9)2+ (–9)2+ (9)2) = √(81 + 81 + 81) = √(243) =

√(3 * 81) = √(3) * √(81) = 9√(3)

Example Question #2 :How To Find The Diagonal Of A Cube

你有一个矩形框尺寸6英寸s by 6 inches by 8 inches. What is the length of the shortest distance between two non-adjacent corners of the box?

Possible Answers:

\dpi{100} \small 6\sqrt{2}

\dpi{100} \small 8\sqrt{2}

\dpi{100} \small 6

\dpi{100} \small 4\sqrt{3}

\dpi{100} \small 8

Correct answer:

\dpi{100} \small 6\sqrt{2}

Explanation:

The shortest length between any two non-adjacent corners will be the diagonal of the smallest face of the rectangular box. The smallest face of the rectangular box is a six-inch by six-inch square. The diagonal of a six-inch square is\dpi{100} \small 6\sqrt{2}

Example Question #3 :How To Find The Diagonal Of A Cube

What is the length of the diagonal of a cube with side lengths ofeach?

Possible Answers:

Correct answer:

Explanation:

The diagonal length of a cube is found by a form of the distance formula that is akin to the Pythagorean Theorem, though with an additional dimension added to it. It is:

, or, or

Now, if the the value ofis, we get simply

Example Question #4 :How To Find The Diagonal Of A Cube

What is the length of the diagonal of a cube that has a surface area of?

Possible Answers:

Correct answer:

Explanation:

To begin, the best thing to do is to find the length of a side of the cube. This is done using the formula for the surface area of a cube. Recall that a cube is made up ofsquares. Therefore, its surface area is:

, whereis the length of a side.

Therefore, for our data, we have:

Solving for, we get:

This means that

Now, the diagonal length of a cube is found by a form of the distance formula that is akin to the Pythagorean Theorem, though with an additional dimension added to it. It is:

, or, or

Now, if the the value ofis, we get simply

Example Question #1 :How To Find The Volume Of A Cube

What is the volume of a rectangular box that is twice as long as it is high, and four times as wide as it is long?

Possible Answers:

4L3

2L2

5L

8

2L3

Correct answer:

2L3

Explanation:

The box is 2 times as long as it is high, soH=L/2. It is also 4 times as wide as it is long, soW= 4L。Now we need volume =L*W*H=L* 4L*L/2 = 2L3

Example Question #2 :Cubes

What is the volume of a cube with a surface area of?

Possible Answers:

Correct answer:

Explanation:

The surface area of a cube is merely the sum of the surface areas of the方块组成它的脸。因此,届e surface area equation understandably is:

, whereis the side length of any one side of the cube. For our values, we know:

Solving for, we get:

or

Now, the volume of a cube is defined by the simple equation:

For, this is:

Example Question #3 :Cubes

The volume of a cube is。我f the side length of this cube is tripled, what is the new volume?

Possible Answers:

Correct answer:

Explanation:

Recall that the volume of a cube is defined by the equation:

, whereis the side length of the cube.

Therefore, if we know that, we can solve:

This means that

Now, if we tripleto, the new volume of our cube will be:

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