Cones, Cylinders, & Spheres Unit Test

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Question
Eli is making a model castle out of clay. One of the roof peaks is in the shape of a cone with a diameter of 14 inches and a slant height of 20 inches. What is the surface area of the cone peak? Round your answer to the nearest hundredth. Use 3.14 for pi.(1 point)
square inches
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1 answer

To find the surface area of the cone peak, we need to use the formula for the lateral surface area of a cone and add the area of the base:

  1. Lateral Surface Area of the Cone:

    \[ \text{Lateral Surface Area} = \pi r l \]

    where \( r \) is the radius and \( l \) is the slant height.

  2. Area of the Base of the Cone:

    \[ \text{Base Area} = \pi r^2 \]

  3. Total Surface Area:

    \[ \text{Total Surface Area} = \text{Lateral Surface Area} + \text{Base Area} \]

Now, we need to calculate the radius \( r \) since we are given the diameter. The diameter is 14 inches, so the radius is:

\[ r = \frac{d}{2} = \frac{14}{2} = 7 \text{ inches} \]

Given:

  • \( r = 7 \) inches
  • \( l = 20 \) inches
  • \( \pi \approx 3.14 \)

Now, we will compute the lateral surface area first:

\[ \text{Lateral Surface Area} = \pi r l = 3.14 \cdot 7 \cdot 20 \]

Calculating that:

\[ \text{Lateral Surface Area} = 3.14 \cdot 7 = 21.98 \]

\[ 21.98 \cdot 20 = 439.6 \text{ square inches} \]

Next, we find the area of the base:

\[ \text{Base Area} = \pi r^2 = 3.14 \cdot (7^2) = 3.14 \cdot 49 \]

Calculating that:

\[ \text{Base Area} = 3.14 \cdot 49 = 153.86 \text{ square inches} \]

Finally, we add the lateral surface area and the base area to find the total surface area of the cone:

\[ \text{Total Surface Area} = \text{Lateral Surface Area} + \text{Base Area} \]

Calculating that:

\[ \text{Total Surface Area} = 439.6 + 153.86 = 593.46 \text{ square inches} \]

Therefore, the surface area of the cone peak is:

\[ \boxed{593.46} \text{ square inches} \]