2 / 1 = 2
(2 + 1) / 2 = 1.5
2 / 1.5 = 1.333333
(1.333333 + 1.5) / 2 = 1.4167
2 / 1.4167 = 1.4118
( 1.4167 / 1.4118 ) / 2 = 1.4142
etc.
The more times you perform the above procedure, the more accurate your answer.