Answer:
Pi—which is written as the Greek letter for p, or π—is the ratio of the circumference of any circle to the diameter of that circle. Regardless of the circle's size, this ratio will always equal pi(3.1415).
There are two radii in one diameter. The formula for circumference is pi*d when using diameter which explains the two in front of the formula given by your teacher.
Step-by-step explanation: