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A cone is made from a sector of a circle with a radius of 14 cm and an angle of 90°. What is the area of the curved surface of the cone?

Sagot :

Let's solve the problem step-by-step:

1. Given Data and Information:
- Radius of the sector (which becomes the slant height of the cone): [tex]\( r = 14 \)[/tex] cm
- Angle of the sector: [tex]\( \theta = 90^\circ \)[/tex]

2. Determine the Arc Length of the Sector:
The arc length (L) of the sector can be calculated using the formula:
[tex]\[ L = 2 \pi r \left( \frac{\theta}{360} \right) \][/tex]
Plugging in the values:
[tex]\[ L = 2 \pi \cdot 14 \left( \frac{90}{360} \right) = 2 \pi \cdot 14 \left( \frac{1}{4} \right) = \pi \cdot 7 \][/tex]
Numerically:
[tex]\[ L \approx 21.991148575128552 \text{ cm} \][/tex]

3. Find the Radius of the Cone's Base:
The radius [tex]\(R\)[/tex] of the base of the cone is the same as the arc length divided by [tex]\(2\pi\)[/tex]:
[tex]\[ R = \frac{L}{2\pi} = \frac{21.991148575128552}{2\pi} \][/tex]
Numerically:
[tex]\[ R \approx 3.5 \text{ cm} \][/tex]

4. Slant Height of the Cone:
The slant height [tex]\(s\)[/tex] of the cone is given by the radius of the original sector:
[tex]\[ s = 14 \text{ cm} \][/tex]

5. Lateral (Curved) Surface Area of the Cone:
The lateral surface area [tex]\(A\)[/tex] of the cone can be determined using the formula:
[tex]\[ A = \pi R s \][/tex]
Plugging in the values:
[tex]\[ A = \pi \cdot 3.5 \cdot 14 \approx 153.93804002589985 \text{ cm}^2 \][/tex]

Therefore, the lateral surface area of the cone is approximately [tex]\( 153.938 \text{ cm}^2 \)[/tex].