The radius of the base of a cone is 4 cm and slant height is 5cm. Its CSA is `:`

Options

A. 20 `cm^(2)`
B. `20 pi cm^(2)`
C. `30 pi cm^(2)`
D. `80 pi cm^(2)`

Answer

To find the curved surface area (CSA) of a cone, we can use the formula:

\[ \text{CSA} = \pi r l \]

where:
- \( r \) is the radius of the base of the cone,
- \( l \) is the slant height of the cone.

### Step-by-Step Solution:

1. **Identify the given values**:
- Radius \( r = 4 \) cm
- Slant height \( l = 5 \) cm

2. **Substitute the values into the CSA formula**:
\[ \text{CSA} = \pi \times r \times l \]
\[ \text{CSA} = \pi \times 4 \times 5 \]

3. **Calculate the product**:
\[ \text{CSA} = \pi \times 20 \]

4. **Express the final answer**:
\[ \text{CSA} = 20\pi \text{ cm}^2 \]

Thus, the curved surface area of the cone is \( 20\pi \text{ cm}^2 \).