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[perfectspring]

Jamie (or anyone else who knows what this means) first question: what does this mean?
Find

Comments

[darth_phoenix]

3rd derivative of y with respect to x, any other variables are considered constants (although it doesn't matter here since you only HAVE one variable).

answer is below... if you have white background, highlight to read...

Mathematica says:
-384*(3x-4)/(4x+2)^4+288/(4x+2)^3

for an input of "D[(3x - 4)/(4x + 2), {x, 3}]", if that helps any. ;)

[perfectspring]

I can't get the first half to save my life... is this the right second derivative?
(288x-32)/(4x+2)^3

[darth_phoenix]

First derivative: 11/(2[2x+1]^2)

Second derivative: -22/[2x+1]^3

Third derivative: 132/[2x+1]^4

[perfectspring]

er... i think i must have forgotten how to find derivatives :-/

[darth_phoenix]

Yeh I know... but they're the same thing, just simplified. I forgot to simplify it last time. And (2x+1) is half of (4x+2), so I'm sure somet cancelled.

[perfectspring]

yeah, i finally got that... and realized that i was putting + instead of - :-P... but i think i finally remembered everything, and i STILL can't see how the second diff is negative.. i have the right answer, but it's positive

[darth_phoenix]

It's 'cause you have a negative power of x.. so you multiply by the negative power when you differentiate. Thus making the second differential negative and the third positive.

[perfectspring]

OHHHH duh... i'm going to be in trouble when school starts :-/