∫ The circumference of an arc AB=⊙O O o.
∴ arc AB=πd
∫ arc AB = 2π a (∠ 1/360)?
∴2πa(∠ 1/360 )=πd?
∴2a(∠ 1/360 )=d?
Bring a and d into 2a(≈ 1/360)= d to get the value of ∠ 1.
In this way, all the data needed to draw the expansion diagram are obtained. According to the data, we can draw the expansion diagram of the cone.