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C3 - Differentiation

Okay.. this has popped up quite a few times. I've simplified and simplified to get dydx=245\frac{dy}{dx}=\frac{2\sqrt{4}}{5}. Now, my understanding is that the answer is + or - 0.8, however, whenever I get a square root in a differential equation, they always only list the positive answer. Am I wrong in saying that dy/dx has two values here?
Reply 1
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Goldfishy
8
Original post by ViralRiver
Okay.. this has popped up quite a few times. I've simplified and simplified to get dydx=245\frac{dy}{dx}=\frac{2\sqrt{4}}{5}. Now, my understanding is that the answer is + or - 0.8, however, whenever I get a square root in a differential equation, they always only list the positive answer. Am I wrong in saying that dy/dx has two values here?


Unparseable latex formula:

\sqrt

is defined as the positive square root, so only the positive answer is given. You only really get ± \pm in things like x2=4 x^2 = 4 , etc.
Reply 2
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ViralRiver
OP
16
So would saying x2=4⇒x=4x^2=4\Rightarrow x=\sqrt{4} be incorrect?
Reply 3
Avatar for Goldfishy
Goldfishy
8
Original post by ViralRiver
So would saying x2=4⇒x=4x^2=4\Rightarrow x=\sqrt{4} be incorrect?


Kind of. It's more x2=4⇒x=±4x^2=4\Rightarrow x= \pm\sqrt{4}

EDIT: Square roots (beginning of 3rd paragraph)
(edited 13 years ago)
Reply 4
Avatar for ViralRiver
ViralRiver
OP
16
Okay, thanks a lot :smile: .

I'd +rep but I'm out >< .

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