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

a cone with a base circumference of about 126 mm

Step-by-step explanation:

Rotating a triangle about a line results in a cone created by the rotation.  This is because the segment at the bottom forms a circle, and the point at the top stays there; the three-dimensional figure with a circular base and a point at the top is a cone.

Since we rotate the segments about a line, this makes the length of the base the radius of the circle. This means the circumference would be

C = 2πr = 2(3.14)(20) = 125.6 ≈ 126 mm