Calculators and computers use Newton's Method to compute square
roots. On this slide, we'll see how to compute $\sqrt{2}$.
Finding the square root of 2 is the same thing as solving $x^2 -
2 = 0$. So we set $f(x)=x^2-2$, $f'(x)=2x$, and apply the
recursive formula $$x_{n+1} = x_n - \frac{f(x_n)}{f'(x_n)} = x_n -
\frac{x_n^2-2}{2x_n}.$$ It only takes a few steps to get 10 or 20
decimal places.