Is 11/12 greater than 4/8

Triangle xyz has vertices x(1,3), y(0,0)

The measure of angle 0 is 600 degrees

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}400? m. what is the diameter dd of the lake?