If you use

r

To represent the bottom radius, l

Represents the generatrix of the cone, and n represents the central angle of the sector on the side of the cone.

Degree, the bottom circumference is

2πr, so the arc length of the sector is also.

2πr and arc length (sector

Circumference) equals

N/360。 The circle occupied by the sector is based on the bus.

l

Is the radius, so it is.

The circumference is

2πr, draw a conclusion

n/360

=

2πr/2πl

=

r/l

r/

l

It is the ratio of the length of the arc to the circumference of the circle occupied by the sector, that is, the sector and the area of the circle occupied by the sector.

Than. Therefore, it is only necessary to multiply the area of the circle occupied by the sector by it.

r/l

You can get the area of the fan. but

The area of a circle occupied by a sector is

πl2, you can get:

s

One side, one side

=

πl2×r/l

=

πrl

Step forward and get the formula for calculating the sector area:

s

One side, one side

=πrl

= 1/2×2πr×l

=

1/2× bottom arc length×

Bus length

It can be inferred from this that the sector area of the cone side is equal to

πrl

be equal to

3. 14

Multiply by the radius of the bottom surface, and then multiply by the matrix.

A thread will do. The surface area of a cone is the side area plus the bottom area, which is:

s

table

=

s

Side +s

bottom

=πrl+πr2

=πrl+πr×r

=πr(l+r)

The formula for calculating the surface area of the cone is obtained. In this way, when making a cone, the side can be determined according to the bottom circle.

The degree of the central angle of a sector can also be used to know its surface area without cutting a cone.