So 65π= 1/2*L* 13.

L= 10π

That is, the arc length of the cone-side expansion diagram is 10π.

Because the perimeter of the bottom circle = the arc length in the expanded diagram.

So 2πR= 10π.

R=5

That is, the radius of the circle at the bottom of the cone =5.

So the height of the cone = √ 13 -5 = 12cm.

2) Sector area =nπr? /360= 1/2Lr

Sector arc length =nπr/ 180