У 9-
8-
7+
6+
5+
4+
3+
2+
1+
-9 -8 -7 -6 -5 -4 -3 -2
2 3 4 5 6 7 8 9
-2+
-3-
-4+
-5+
-6+
-7+
-8
-9

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?