• UnRelatedBurner@sh.itjust.worksEnglish
        291·
        7 months ago

        Uhm, actually 🤓☝️!

        Afaik sqrt only returns positive numbers, but if you’re searching for X you should do more logic, as both -3 and 3 squared is 9, but sqrt(9) is just 3.

        If I’m wrong please correct me, caz I don’t really know how to properly write this down in a proof, so I might be wrong here. :p
        (ps: I fact checked with wolfram, but I still donno how to split the equation formally)

        • criitz@reddthat.comEnglish
          24·
          7 months ago

          You’re correct. The square root operator only returns the principal root (the positive one).

          So if x^2 = 9 then x = ±√9 = ±3

          That’s why in something like the quadratic formula we all had to memorize in school its got a “plus or minus” in it: -b ± √…(etc)

          • Routhinator@startrek.websiteEnglish
            21·
            7 months ago

            So I checked this on my smartphone first, and thought maybe the software is just shit… So then I checked it on a Casio scientific calc, and both agree.

            -3^2 = -9… And 9 != -9

            … Are all the calculators somehow wrong? What’s the math rule I’m forgetting here…

                • Routhinator@startrek.websiteEnglish
                  1·
                  7 months ago

                  GD I am just realizing how long its been since I did math in my head without a programming language…

                  I should take a math class again or something and refresh that knowledge.

        • h3ndrik@feddit.deEnglish
          22·
          7 months ago

          x^2 = 9

          <=>

          |x| = sqrt(9)

          would be correct. That way you get both 3 and -3 for x.

          That’s the way your math teacher would do it. So the correct version of the statement in the picture is: “if x^2 = 9 then abs(x) = 3”