### All High School Math Resources

## Example Questions

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

What is the surface area of a cone with a radius of 4 and a height of 3?

**Possible Answers:**

**Correct answer:**

Here we simply need to remember the formula for the surface area of a cone and plug in our values for the radius and height.

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

The lateral area is twice as big as the base area of a cone. If the height of the cone is 9, what is the entire surface area (base area plus lateral area)?

**Possible Answers:**

27π

90π

54π

9π

81π

**Correct answer:**

81π

Lateral Area = LA = π(r)(l) where r = radius of the base and l = slant height

LA = 2B

π(r)(l) = 2π(r^{2})

rl = 2r^{2}

l = 2r

From the diagram, we can see that r^{2} + h^{2} = l^{2}. Since h = 9 and l = 2r, some substitution yields

r^{2} + 9^{2} = (2r)^{2}

r^{2} + 81 = 4r^{2}

81 = 3r^{2}

27 = r^{2}

B = π(r^{2}) = 27π

LA = 2B = 2(27π) = 54π

SA = B + LA = 81π

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

What is the surface area of a cone with a height of 8 and a base with a radius of 5?

**Possible Answers:**

**Correct answer:**

To find the surface area of a cone we must plug in the appropriate numbers into the equation

where is the radius of the base, and is the lateral, or slant height of the cone.

First we must find the area of the circle.

To find the area of the circle we plug in our radius into the equation of a circle which is

This yields .

We then need to know the surface area of the cone shape.

To find this we must use our height and our radius to make a right triangle in order to find the lateral height using Pythagorean’s Theorem.

Pythagorean’s Theorem states

Take the radius and height and plug them into the equation as a and b to yield

First square the numbers

After squaring the numbers add them together

Once you have the sum, square root both sides

After calculating we find our length is

Then plug the length into the second portion of our surface area equation above to get

Then add the area of the circle with the conical area to find the surface area of the entire figure

The answer is .

### Example Question #1041 : Act Math

What is the surface area of a cone with a radius of 6 in and a height of 8 in?

**Possible Answers:**

36*π* in^{2}

96*π* in^{2}

112*π* in^{2}

66*π* in^{2}

60*π* in^{2}

**Correct answer:**

96*π* in^{2}

Find the slant height of the cone using the Pythagorean theorem: *r*^{2} + *h*^{2} = *s*^{2} resulting in 6^{2} + 8^{2} = *s*^{2} leading to *s*^{2} = 100 or *s* = 10 in

SA = *πrs* + *πr*^{2} = *π*(6)(10) + *π*(6)^{2} = 60*π* + 36*π* = 96*π* in^{2}

60*π* in^{2} is the area of the cone without the base.

36*π* in^{2} is the area of the base only.

### Example Question #2 : How To Find The Surface Area Of A Cone

Find the surface area of a cone that has a radius of 12 and a slant height of 15.

**Possible Answers:**

**Correct answer:**

The standard equation to find the surface area of a cone is

where denotes the slant height of the cone, and denotes the radius.

Plug in the given values for and to find the answer:

### Example Question #2 : How To Find The Surface Area Of A Cone

Find the surface area of the following cone.

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone is:

where is the radius of the cone and is the slant height of the cone.

Plugging in our values, we get:

### Example Question #4 : How To Find The Surface Area Of A Cone

Find the surface area of the following cone.

**Possible Answers:**

**Correct answer:**

The formula for the surface area of a cone is:

Use the Pythagorean Theorem to find the length of the radius:

Plugging in our values, we get:

### Example Question #5 : How To Find The Surface Area Of A Cone

Find the surface area of the following half cone.

**Possible Answers:**

**Correct answer:**

The formula for the surface area of the half cone is:

Where is the radius, is the slant height, and is the height of the cone.

Use the Pythagorean Theorem to find the height of the cone:

Plugging in our values, we get: