Cubes - High School Math

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Question

Find the length of the diagonal connecting opposite corners of a cube with sides of length $2\sqrt{2}$ .

Answer

Find the diagonal of one face of the cube using the Pythagorean Theorem applied to a triangle formed by two sides of that face ( and ) and the diagonal itself ():

$(2\sqrt{2})^2 + (2\sqrt{2})^2 = c^2$

$\rightarrow 8 + 8 = c^2$

$\rightarrow 16 = c^2$

$\rightarrow c = 4$

This diagonal is now the base of a new right triangle (call this ). The height of that triangle is an edge of the cube that runs perpendicular to this diagonal (call this ). The third side of the triangle formed by and is a line from one corner of the cube to the other, i.e., the cube's diagonal (call this ). Use the Pythagorean Theorem again with the triangle formed by , , and to find the length of this diagonal.

$(2\sqrt{2})^2 + (4)^2 = c^2$

$\rightarrow 8 + 16 = c^2$

$\rightarrow 24 = c^2$

$\rightarrow \sqrt{24} = c$

$\rightarrow c= 2\sqrt{6}$

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Question

Find the length of the diagonal of the following cube:

Answer

To find the length of the diagonal, use the formula for a triangle:

$a-a-a\sqrt{2}$

$4\ m-4\ m-4\sqrt{2}\ m$

The length of the diagonal is $4\sqrt{2}\ m$ .

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Question

Our backyard pool holds 10,000 gallons. Its average depth is 4 feet deep and it is 10 feet long. If there are 7.48 gallons in a cubic foot, how wide is the pool?

Answer

There are 7.48 gallons in cubic foot. Set up a ratio:

1 ft3 / 7.48 gallons = x cubic feet / 10,000 gallons

Pool Volume = 10,000 gallons = 10,000 gallons * (1 ft3/ 7.48 gallons) = 1336.9 ft3

Pool Volume = 4ft x 10 ft x WIDTH = 1336.9 cubic feet

Solve for WIDTH:

4 ft x 10 ft x WIDTH = 1336.9 cubic feet

WIDTH = 1336.9 / (4 x 10) = 33.4 ft

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Question

A cube has a volume of 64cm3. What is the area of one side of the cube?

Answer

The cube has a volume of 64cm3, making the length of one edge 4cm (4 * 4 * 4 = 64).

So the area of one side is 4 * 4 = 16cm2

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Question

Given that the suface area of a cube is 72, find the length of one of its sides.

Answer

The standard equation for surface area is

where denotes side length. Rearrange the equation in terms of to find the length of a side with the given surface area:

$a=\sqrt{\frac{SA}{6}}=\sqrt{\frac{72}{6}}=\sqrt{12}=2\sqrt{3}$

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Question

Find the length of an edge of the following cube:

The volume of the cube is $27\ m^3$ .

Answer

The formula for the volume of a cube is

,

where is the length of the edge of a cube.

Plugging in our values, we get:

$27\ m^3 = (e)^3$

$e = 3\ m$

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Question

Find the length of an edge of the following cube:

The volume of the cube is $64\ m^3$ .

Answer

The formula for the volume of a cube is

,

where is the length of the edge of a cube.

Plugging in our values, we get:

$64\ m^3=(e)^3$

$e=4\ m$

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Question

What is the length of an edge of a cube that has a surface area of 54?

Answer

The surface area of a cube can be determined using the following equation:

$SA=6\times l^2$

$\frac{54}{6}=\frac{6l^2}{6}$

$\sqrt9=\sqrt{l^2}$

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Question

If the surface area of a cube equals 96, what is the length of one side of the cube?

Answer

The surface area of a cube = 6a2 where a is the length of the side of each edge of the cube. Put another way, since all sides of a cube are equal, a is just the lenght of one side of a cube.

We have 96 = 6a2 → a2 = 16, so that's the area of one face of the cube.

Solving we get √16, so a = 4

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Question

A sphere with a volume of $\frac{32}{3}$ $\pi m^{3}$ is inscribed in a cube, as shown in the diagram below.

What is the surface area of the cube, in $m^{2}$ ?

Answer

We must first find the radius of the sphere in order to solve this problem. Since we already know the volume, we will use the volume formula to do this.

$V_{sphere}=\frac{4}{3}\pi r^{3}$

$\frac{32}{3}\pi =\frac{4}{3}\pi r^{3}$

$\frac{32}{3}=\frac{4}{3}r^{3}$

$\frac{3}{4}\cdot \frac{32}{3}= r^{3}$

$8=r^{3}$

With the radius of the sphere in hand, we can now apply it to the cube. The radius of the sphere is half the distance from the top to the bottom of the cube (or half the distance from one side to another). Therefore, the radius represents half of a side length of a square. So in this case

$side=2\cdot 2=4$

The formula for the surface area of a cube is:

$SA_{cube}=6s^{2}$

$6s^{2}=6\cdot (4)^{2}=6\cdot 16=96$

The surface area of the cube is $96\ m^{2}$

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Question

What is the surface area of a cube if its height is 3 cm?

Answer

The area of one face is given by the length of a side squared.

$A_{face}=(3cm)^2=9\ cm^2$

The area of 6 faces is then given by six times the area of one face: 54 cm2.

$A_{total}=6(A_{face})=6(9\ cm^2)=54\ cm^2$

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Question

The side of a cube has a length of $\dpi{100} \small 5 cm$ . What is the total surface area of the cube?

Answer

A cube has 6 faces. The area of each face is found by squaring the length of the side.

$\dpi{100} \small 5\times 5 = 25$

Multiply the area of one face by the number of faces to get the total surface area of the cube.

$\dpi{100} \small 25 \times 6=150$

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Question

What is the surface area of a cube with a side length of ?

Answer

To find the surface area of a cube, we must count the number of surface faces and add the areas of each together. In a cube there are faces, each a square with the same side lengths. In this example the side length is .

The area of a square is given by the equation . Using our side length, we can solve the area of once face of the cube.

$A=(7)^{2}=49$

We then multiply this number by , the number of faces of the cube to find the total surface area.

Our answer for the surface area is .

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Question

What is the surface area of a cube with a side length of 15?

Answer

To find the surface area of a cube we must count the number of surface faces and add the areas of each of them together.

In a cube there are 6 faces, each a square with the same side lengths.

In this example the side lengths is 15 so the area of each square would be

We then multiply this number by 6, the number of faces of the cube, to get

Our answer for the surface area is .

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Question

If a right triangle has a hypotenuse of length 5, and the length of the other sides are and , what would be the surface area of a cube having side length ?

Answer

By the Pythagorean Theorem,

$x=\sqrt{5}$

The surface area of a cube having 6 sides, is 6 times the area of one of its sides.

The area of any side of a cube is the square of the side length.

So if the side length is , the area of any side is , or .

Thus the surface area of the cube is

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Question

What is the surface area of a cube with a side length of ?

Answer

In order to find the surface area of a cube, use the formula $SA=6(s^{2})$ .

$SA=6(7.2in)^{2}$

$SA=651.84in^{2}$

$SA=311.04in^{2}$

$\rightarrow 311in^{2}$

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Question

What is the surface area, in inches, of a rectangular prism with a length of $\dpi{100} l=2.2ft$ , a width of , and a height of ?

Answer

In order to find the surface area of a rectangular prism, use the formula .

However, all units must be the same. All of the units of this problem are in inches with the exception of $\dpi{100} l=2.2ft$ .

Convert to inches.

$l=\frac{2.2ft}{1}*\frac{12in}{1ft}$

Now, we can insert the known values into the surface area formula in order to calulate the surface area of the rectangular prism.

$SA=(950.4in^{2})+(504in^{2})+(739.2in^{2})$

$SA=2193.6in^{2}$

If you calculated the surface area to equal $6652.8in^{2}$ , then you utilized the volume formula of a rectangular prism, which is ; this is incorrect.

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Question

$\textup{What is the surface area, in terms of }p,\textup{of a cube with sides of length }p\textup{ ?}$

Answer

$\textup{Each of the six identical faces of the cube is a square with sides }p.$

$\textup{Each face: }A=p^{2}: : : : : \textup{Surface area}=6p^{2}$

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Question

What is the surface area of a cube with a diagonal of $\dpi{100} d=4.2cm$ ?

Answer

A few facts need to be known to solve this problem. Observe that the diagonal of the square face of the cube cuts it into two right isosceles triangles; therefore, the length of a side of the square to its diagonal is the same as an isosceles right triangle's leg to its hypotenuse: $1:\sqrt{2}$ .

$\frac{s}{d}=\frac{1}{\sqrt{2}}$

$\dpi{100} \dpi{100} \frac{s}{4.2cm}=\frac{1}{\sqrt{2}}$

Rearrange an solve for .

$\dpi{100} s=\frac{4.2cm}{\sqrt{2}}$

Now, solve for the area of the cube using the formula $\dpi{100} \dpi{100} SA=6(s^{2})$ .

$SA=6(\frac{4.2cm}{\sqrt{2}})^{2}$

$SA=\frac{6}{1}(\frac{4.2cm}{\sqrt{2}}\frac{4.2cm}{\sqrt{2}})$

$\dpi{100} SA=\frac{6}{1}(\frac{17.64cm^{2}}{2})$

$\dpi{100} \dpi{100} SA=3*17.64cm^{2}$

$\rightarrow 52.92cm^{2}$

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Question

This figure is a cube with one face having an area of 16 in2.

What is the surface area of the cube (in2)?

Answer

The surface area of a cube is the sum of the area of each face. Since there are 6 faces on a cube, the surface area of the entire cube is $6\cdot16$ .

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