From: Pat Ballew (for Teacher2Teacher Service)
Date: May 16, 2000 at 23:11:15
Subject: Re: How do you explain how to do square roots over 100?

There are several approaches to finding square roots by hand.  For
inexperienced students (those still struggling to understand the ideas) I
like guess and test.  It helps them with concepts and estimation skills.

  To find the square root of 215 I try to guess an answer... and since it is
more than 100, I will guess something bigger than ten.. maybe 20 works ....
 is 20^2 = 215???? nope, it's 400, too big so I need to guess a smaller
number....
  15????  15^2 = 225......OOOH very close, just a little big, maybe 14 will
work
   drats!!! 14^ is only 196.. but at least I know the answer is between 14
and 15... so I try 14.5....

of course you see how this goes and at some point we say close enough,
because the real root is irrational and will never end... (a big discovery
when we first make it).. ..

There are other ways, divide and average is a good one...

I think all of the methods are given on the web page at the Dr. Math FAQ
page, Here is the URL for square roots by hand...

http://mathforum.org/dr.math/faq/faq.sqrt.by.hand.html

good luck, hope this gives you some ideas for your class.


 -Pat Ballew, for the Teacher2Teacher service

Post a public discussion message
Ask Teacher2Teacher a new question