Estimate Pi by approximating the area of a circle. How: generate N random numbers in the unit square, (0,0) to (1,1) and see how are within a radius of 1 or less, i.e.
sqrt(x^2 + y^2) < r
since the radius is 1.0, we can square both sides and avoid a sqrt() computation:
x^2 + y^2 <= 1.0
this area under the curve is (Pi * r^2)/ 4.0, and the area of the unit of square is 1.0, so Pi can be approximated by
# points with x^2+y^2 < 1 Pi =~ -------------------------- * 4.0 total # points