this post was submitted on 17 Apr 2024
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Science Memes

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teachings (mander.xyz)
submitted 7 months ago by [email protected] to c/[email protected]
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[โ€“] [email protected] 29 points 7 months ago (2 children)

Uhm, actually ๐Ÿค“โ˜๏ธ!

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)

[โ€“] [email protected] 25 points 7 months ago* (last edited 7 months ago) (2 children)

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

So if x^2 = 9 then x = ยฑโˆš9 = ยฑ3

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 ยฑ โˆš...(etc)

[โ€“] [email protected] 1 points 7 months ago (1 children)

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...

[โ€“] [email protected] 5 points 7 months ago (1 children)

I think your calculator is interpreting that as -(3^2) and not (-3)^2

[โ€“] [email protected] 3 points 7 months ago (1 children)

Oh derp. Yep it is.

Was better when calcs had a +/- button.

And I remembered the math rule too.

[โ€“] [email protected] 1 points 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.

[โ€“] [email protected] 9 points 7 months ago

Thanks, I haven't connected the dots to that (+-) sign and this problem.

[โ€“] [email protected] 21 points 7 months ago* (last edited 7 months ago) (1 children)

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"

[โ€“] [email protected] 4 points 7 months ago

Cool! Makes sense to me. Honestly, I've never done it this way, but it's so clean. Love it. Thanks.