how does the square root of 25^2-15^2 equal 20?

Hi,

 

let's break the problem apart into digestable chunks:

 

25^2 = 25 * 25 = 625

 

15^2 = 15 * 15 = 225

 

Therefore

25^2 - 15^2 = 625 - 225

 

625 - 225 = 400

 

The square root of 400 is 20 because

20 * 20 = 400

 

Hope that helped.