You are standing next to a really big circular lake. You want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! You decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400π m400, pi, start text, space, m, end text. What is the diameter ddd of the lake?
d=d=d, equals
\text{m}mstart text, m, end text