hi there,

i am not sure what is the answer you wrote there but here is how i will do it:

Given a circle of radius 5 cm and a sector of is taken out,

Circumference of the circle without the cut off =

Circumference of the circle with the cut off =

where,

= arc length =

in radians

therefore,

Circumference of the circle with the cut off

this circumference of the circle with the cut off is actually the circumference of the circle of the cone itself:

therefore,

circumference of circle of cone

where R = radius of the circle of the cone

the height of the cone can be found using Pythagoras theorem: (view attachment)

now that you have the radius, R and the height of the cone you can simply substitute them into the volume of a cone formula: