A point P is randomly selected from the square region with vertices at $(\pm 1, \pm 1)$. What is the probability that P is within one unit of the origin? Express your answer as a common fraction in terms of pi.
The probability of being within one unit of the origin is the area within a circle centered at the origin with
a radius of 1 divided by the area of a square with side lengths of 2.
The area of the circle is: pi · r2 = pi · 12 = pi.
The area of the square is 2 · 2 = 4
The probability is pi / 4