My Math Forum Positive or negative root

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 August 31st, 2017, 06:22 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. Thanks from verygoodatmaths
 August 31st, 2017, 06:28 PM #2 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,958 Thanks: 1146 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. Thanks from QEDboi and verygoodatmaths
 August 31st, 2017, 06:29 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 Thanks from QEDboi, verygoodatmaths and Dylyduck
 September 1st, 2017, 07:20 AM #4 Senior Member   Joined: Aug 2017 From: United Kingdom Posts: 313 Thanks: 112 Math Focus: Number Theory, Algebraic Geometry Just to add to this, when we write $\sqrt{a}$ (where $a$ is a non-negative real number), we are referring specifically to the non-negative 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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