Question

the circumference of a circle is equal to π multiplied by ______ ?
the diameter
the radius
half the radius
twice the diameter

Explanation:

The formula for the circumference \( C \) of a circle is \( C=\pi d \) (where \( d \) is the diameter) or \( C = 2\pi r \) (where \( r \) is the radius). From \( C=\pi d \), we see the circumference is \( \pi \) multiplied by the diameter. The other options: radius would give \( 2\pi r \) (so circumference is \( 2\pi \) times radius, not \( \pi \) times radius), half the radius is incorrect, and twice the diameter would be \( 2d \), so \( \pi\times2d = 2\pi d \), which is not the standard circumference formula. So the correct option is "The diameter".

Answer:

A. The diameter