Let R be a rectangle, and let P be a point which lies out- side R. Show how one may construct a line ` which passes through P and divides R into two pieces of equal content. Prove that your construction is correct.

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?