Description: Learn how to approximate the decimal value of the square root of 45 without using a calculator. Created by Sal Khan and Monterey Institute for Technology and Education. We are asked to approximate the principal root, or the positive square root of 45, to the hundredths place. So, let's see if we can approximate this just with our pen and paper right over here. It's definitely not a perfect square.*Teacher Advisor is 100% free.