Biologists conducted a 20 year study of fruit bat populations in a small African country. The polynomial function p(x) models of the fruit bat population from the year 1990 (when x=0) to the year 2010 (when x=20)

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?