Dealing v the concerns of attributes in eleventh course my gimpppa.orgs teacher claims that square root of a genuine number is constantly positive. Just how is the possible?


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Given a optimistic real number $a$, there space two options to the equation $x^2 = a$, one is positive, and the various other is negative. We signify the positive root (which us often call the square root) by $sqrta$. The an unfavorable solution of $x^2 = a$ is $-sqrta$ (we understand that if $x$ satisfies $x^2 = a$, then $(-x)^2 = x^2 = a$, therefore, due to the fact that $sqrta$ is a solution, for this reason is $-sqrta$). So, because that $a > 0$, $sqrta > 0$, however there are two options to the equation $x^2 = a$, one hopeful ($sqrta$) and also one an adverse ($-sqrta$). For $a = 0$, the two solutions coincide through $sqrt0 = 0$.

You are watching: Positive numbers have negative square roots true or false


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answered may 26 "14 in ~ 1:01
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Michael AlbaneseMichael Albanese
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It is just a notational matter. Through convention, for optimistic $x$ (real clearly), $sqrtx$ denotes the positive square root of the genuine number $x$. Similarly we agree by way of notational convention that $-sqrtx$ is the an unfavorable square root of $x$. The course, every confident real number, $x$, has two square roots, $sqrtx$ and $-sqrtx$, hopeful and an unfavorable real number respectively.

I problem sometimes about what gets taught by way gimpppa.orgematics in an additional school these days.


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edited might 26 "14 in ~ 7:02
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answered might 26 "14 in ~ 6:34
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Richard GayleRichard Gayle
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Technically this explain is wrong. He might say, "The square root of a positive number is hopeful (by definition)". E.g. For 0 you get $sqrt0=0$ which is neither optimistic nor negative. And also for negative numbers you also get complex solutions which are neither positive nor an adverse nor 0.

The identify article and the singular in "the square root" is additionally important to indicate the conventional meaning of $sqrt$. But much more correctly he must say "the major square root", since gimpppa.orgematically the expression "the square root" doesn"t do sense, due to the fact that there are two different roots in general.


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answered may 26 "14 in ~ 18:18
David OngaroDavid Ongaro
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I think your man is comes from assuming the if $a^2 = b$ climate $sqrtb =a$, but this is actually not the case. The correct form of this would be $sqrtb = vert a vert$. Since of this, $a^2 = b = (-a)^2$ but $sqrtb = vert a vert eq -vert a vert$. This have the right to be proven by contradiction:

If we were to say that $a=sqrtb=-a$, the would because of this imply that $a = -a$, and for instance $1= sqrt1 = -1 implies 1=-1$ which we know to it is in false. This contradiction walk not present up once saying $a^2 = b = (-a)^2 implies a^2 = (-a)^2$, because, if us were to use the same example, us would obtain $1^2 = 1 = (-1)^2 implies 1^2 = (-1)^2 implies 1 = 1$, i m sorry is true (since by definition, any type of number squared must it is in positive). This is why, if you were to evaluate $a^2 = b$, friend would gain two possible equipment for $a$ (one positive, and also one negative). However, if you were to evaluate the equation $a = sqrtb$, $a$ can only have one solution at any kind of given time, and for convention, a square root was defined to constantly be positive. This is crucial distinction due to the fact that it enables us come look in ~ the equation $4=a^2$, and also find that $a=2oplus a=-2$, thus preventing the contradiction $a=2 wedge a=-2 implies 2=-2$ by speak $2^2=4=2^2 implies 2 = 2 oplus (-2)^2=4=(-2)^2 implies -2=-2$. This idea can seem to gain lost as soon as graphing equations such together a circle. The equation $x^2 + y^2 = 1$ appears to have actually 2 $y$ values for every $x$, and also 2 $x$ worths for every $y$. This can be much better understood by instead looking at the parametric equation because that a circle: $x=cos(t); y=sin(t)$. For any given value of $t$, there is only one matching value the $x$, and also only one equivalent value the $y$. If girlfriend are provided a value for $x$, and also told to deal with for $t$, the many you deserve to do is uncover possibilities the $t$, since the $(x,y)$ clues on the graph repeat us every $2pi*t$. The same idea is true because that square roots. As soon as you square a number, it constantly creates a confident number, thus it is difficult to turning back definitively. The most we deserve to do is say that there space two possibilities that what the initial number was. For convention, it has been developed that because that an equation $a^2 = b$, wherein $sqrtb=c$, we say that $c=vert a vert$. The would occupational just as well to characterized a square root by $c=-vert a vert$, however I guess: v the gimpppa.orgematicians that chose on it chosen working with optimistic numbers more.

The point in all of this was to simply develop that taking the square root of a squared number, does no reverse that is exponent, because it cannot be reversed definitively. As user86418 placed it:

If a and also b are actual numbers, climate the conditions $a^2=b$ and $a=sqrtb$ room not logically equivalent; the second implies the first, but not conversely.

See more: Two Integers With The Same Sign, Does The Order In Which You Add Affect The Sum

Therefor, for the purposes of convention, a square root has actually been characterized to be the absolute worth of the original number that was squared. This why, if you plug the attributes $y^2 = x$ and $y = sqrtx$ right into a graphing calculator or Wolfram Alpha, girlfriend will find that you gain two really different looking graphs. Notice how the the graph the $y=sqrtx$ never goes listed below the $x$-axis. Had a square root been identified as constantly negative, the graph of $y=sqrtx$ would just be flipped about the $x$-axis.