Question

The equilateral triangle shown is rotated about line a. Each side of the triangle measures 20 mm.

An equilateral triangle is shown. Line of rotation a goes through one point and the midpoint of the opposite side.

What shape is created by the rotation and what is the approximate circumference of the base?

Circumference of a circle: C = 2πr

a cylinder with a circumference of about 63 mm
a cylinder with a circumference of about 126 mm
a cone with a base circumference of about 63 mm
a cone with a base circumference of about 126 mm