S 1:S2:S3= 1:2:3

N 1: N2: N3 = 1: 2: 3 is deduced.

Arc length formula l=(n/ 180)πR

l 1:L2:L3 = n 1:N2:n3 = 1:2:3

And l 1+l2+l3= circumference C ..

The arc length is the circumference of each cone base: l 1=c 1, l2=c2, l3=c3.

According to the perimeter formula C=2πR

Get R=C/2π.

R=C/2π

r 1=c 1/2π

r2=c2/2π

r3=c3/2π

And c1+C2+C3 = C.

Therefore, r1+R2+R3 = (c1+C2+C3)/2π = c/2π = R.

(2) It is semi-circular after paving.

Solution: Let the bus length be L and the bottom radius be R. ..

Bottom circumference C=2πr=πl

After production, the bus becomes the radius of the fan, and the circumference c becomes the arc length of the fan.

The circumference of a circle with radius l is 2π l.

This arc length =πl=2πl/2

So this figure is a semicircle.

(3) Solution: Let the arc length of the expansion diagram be L and the radius be R. ..

R=20M

Cone base circumference C=30πM

l = C = 30πM & lt； 2πR

So this expansion diagram is a fan.

By the arc length formula l=(n/ 180)πR

Central angle n =180 l/π r =180 * 30 π/20 π = 270.

Area s = (n π r 2)/360 = 400 π * 3/4 = 300 π m 2.