When the side development diagram of the big cone is truncated, the side development of the small cone is truncated.
The differences between these two departments,
The radius of each expanded sector is the length of the generatrix, and the arc is the circumference of the cone bottom.
Calculate the central angle according to the central angle of radian multiplied by the radius equal to the corresponding arc length.
It is known that the main arc m=2πb, the secondary arc n=2πa, and the difference d between the radius r of the main arc and the radius r of the secondary arc.
c=R-r
, find the central angle α.
αr=n，αR=m
Subtract these two expressions.
α=(m-n)/(R-R)=(m-n)/c =(2πb-2πa)/c = 2π(b-a)/c
r=n/α=2πa/α
R=m/α=2πb/α