# Absolutely STUCK on a 2nd derivative

#### mateomy

Absolutely STUCK on a 2nd derivative!!!

1. The problem statement, all variables and given/known data

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#### mateomy

Re: Absolutely STUCK on a 2nd derivative!!!

Thanks for that. Im reading on how to use LaTeX right now. Again, thanks.

#### joeghal87

Re: Absolutely STUCK on a 2nd derivative!!!

Hello there,

here is the problem, your second derivative is wrong it should be:

y"= [2(x^2+x-2)^(1/2)-( {((2x+1)^2)/(2(x^2+x-2)^(1/2))} )] /(2(x^2+x-2))

then what you have to do is multiply by (x^2+x-2)^(1/2) both the numerator and the denominator

thus you'll obtain this form :

y" = (2(x^2+x-2)-(2x+1)^2)/(2(x^2+x-2)^(3/2))

all you have to do now is develop the numerator of this expression and you'll get this :

y" = (-2x^2-2x-5)/(2(x^2+x-2)^(3/2))

here you go, and to get the exact one like the book, u have to multiply by 2 both numerators and denominators... Your book should have done the simplification already though...

#### mateomy

Re: Absolutely STUCK on a 2nd derivative!!!

Hello there,

here is the problem, your second derivative is wrong it should be:

y"= [2(x^2+x-2)^(1/2)-( {((2x+1)^2)/(2(x^2+x-2)^(1/2))} )] /(2(x^2+x-2))

then what you have to do is multiply by (x^2+x-2)^(1/2) both the numerator and the denominator

thus you'll obtain this form :

y" = (2(x^2+x-2)-(2x+1)^2)/(2(x^2+x-2)^(3/2))

all you have to do now is develop the numerator of this expression and you'll get this :

y" = (-2x^2-2x-5)/(2(x^2+x-2)^(3/2))

here you go, and to get the exact one like the book, u have to multiply by 2 both numerators and denominators... Your book should have done the simplification already though...

Thanks, but Im still confused. Why would you want to multiply the denominator and numerator by 2? I know it will make the expression match what I have in the book, but what would be the ultimate purpose (besides and answer match) to doing the multiplication?

Super appreciative for the help, btw.

#### joeghal87

Re: Absolutely STUCK on a 2nd derivative!!!

the purpose : absolutely nothing at all :) actually your book just didn't simplify the expression to the fullest... if you divide by 2 the numerator and deminator in the final expression reached from the book, you get to the one I found... like I said, they should have done the simplification themselves :)

and you're welcome ! anytime :)

#### mateomy

Re: Absolutely STUCK on a 2nd derivative!!!

Thank you so much. I've been pacing around all morning trying to figure out why that looked the way it did.

And now...on to yet more problems.

THANKS!!

"Absolutely STUCK on a 2nd derivative"

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