Calculating square roots of positive numbers in a simple way I'm learning math (for its applications) so this may be obvious. Is there a simple way to calculate the square root of a real number by using a function repeatedly  that uses only plus, minus, add or divide. So after the function is used once the output of that is used as the new input to the second use of the function and so on. When I mean simple it something that can be done by hand on a simple 4 function calculator.
I'd love to know the answer.

I remember that quite a while back in school my teacher did tell me a method to do this, 
lets take '20' as an example, first you choose an estimate square root, I choose 4, then you divide 20 by 4, which gives 5, and then you take the average of 4 and 5; giving 4.5
Then you divide 20 by 4.5, which is 4.44.. and you take the average of 4.5 and 4.44 to get 4.47, (you can continue doing this) 
You see you won't get a perfect answer, but you can get a good estimate if you choose your starting number well.
