Frustum question work out the bottom bit of the cone.

60pi cm^2 = 188.5 cm^2

Step-by-step explanation:

You don't need to understand how or why the curved surface area of a cone is pi×r×L. You just need to see that the answer is area big cone minus area small cone.

big cone curved surface area

B = pi × 8 × 10 cm^2 = 80pi cm^2

small cone dimensions. It's similar to big cone so all dimensions scale by same factor, namely 1/2 ("the height of the small cone is half the height of the large cone.")

small cone curved surface area

S = pi × 8/2 × 10/2 cm^2 = 20pi cm^2

Frustum curved surface area = B - S = 60pi cm^2 = 188.5 cm^2

But if you want to know why the curved surface area is pi r L, take a paper cone with base radius r and slant length L, and cut straight from base to apex. It flattens out to the sector of a circle with radius L and arc length 2pi r.

Now the arc length of a full circle of radius L is 2pi L, and its area is pi L^2. So the area is half arc length (pi L) times radius (L).

Arc length of sector is 2pi r

Half arc length is pi r

Radius is L

Area of sector of circle unrolled from cone is pi r L.

step-by-step explanation:

a line is an defined derm because it

a)contains an infinite number of points b) can be used to create other geometric shapes c)describes something that does not have width or depth d) is a term that does not have a formal definition. a line is an undefined term because it: contains an infinite number of points.