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August 31st, 2017, 07:22 PM  #1 
Newbie Joined: Jun 2017 From: Perth, Australia Posts: 8 Thanks: 7  Positive or negative root
Hey, Just a quick question for advice on how you all remember to do this. Take the example: V^2=4 V=+\square root(4) Excuse the lack of symbols, pretty new to posting online. I always forget to include the plus or minus sign before the square root. Does anyone have a quick mental way to remember, or will it come naturally. 
August 31st, 2017, 07:28 PM  #2 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,743 Thanks: 1001 Math Focus: Elementary mathematics and beyond 
You need to be more careful. Focus on exactly what it is you are doing and think of all possible ways of doing it. Don't feel bad  I have had (and still have, at times) an annoying carelessness  we all do from time to time. Learning by rote may be helpful  do several problems involving squared quantities. 
August 31st, 2017, 07:29 PM  #3 
Newbie Joined: Aug 2017 From: New Zealand Posts: 4 Thanks: 4 
I think you just need to understand why square root(x) = +/x^2. For example, if we take root(4), we need to find what value(s), when squared, equal 4. 2^2 = 2 x 2 =4 (2)^2 = 2 x 2 =4 Hence, root(4) = +/2 Hope I helped 
September 1st, 2017, 08:20 AM  #4 
Senior Member Joined: Aug 2017 From: United Kingdom Posts: 119 Thanks: 38 Math Focus: Algebraic Number Theory, Arithmetic Geometry 
Just to add to this, when we write $\sqrt{a}$ (where $a$ is a nonnegative real number), we are referring specifically to the nonnegative root. The key point is that if you are told $x^2 = a$, this does not imply that $x = \sqrt{a}$  it implies that $x = \sqrt{a}$ or $x = \sqrt{a}$.


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