Question

A cone has radius 3 and height 4. Your classmate calculates its surface area as shown:

Explain your classmate's error.
S. A. = pi(5)^2 + pi(3)^2 = 25pi + 9pi = 3pi

Answer 1

Lateral surface area of cone = π(3)(5)

Lateral surface area of cone = 47.1 unit² (Approx.)

Explanation:

Given:

Radius of cone = 3 unit

Height of cone = 4 unit

Find:

Lateral surface area of cone

Computation:

Slant height of cone = √Radius² + Height²

Slant height of cone = √3² + 4²

Slant height of cone = √9 + 16

Slant height of cone = √25

Slant height of cone = 5 unit

Lateral surface area of cone = πrl

Lateral surface area of cone = π(3)(5)

Lateral surface area of cone = (3.14)(15)

Lateral surface area of cone = 47.1 unit² (Approx.)