Quadrilateral BCDE is dilated by a scale factor of 2 with the center of dilation at the origin. If the coordinates of point B are (2, 1), the coordinates of B' are

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?