Find the derivative of f(x) = -12x2 + 9x at x = 6.
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@ganeshie8 @hero @dan815 @perl @pooja195 @nincompoop @CGGURUMANJUNATH @zepedrix @usukidoll

- anonymous

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- nincompoop

use power rule

- anonymous

how do i do that? can u show me step by step? @nincompoop

- nincompoop

you can get the general derivative first and then apply at x=6 or you can apply it from the beginning

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## More answers

- UsukiDoll

\[f(x) = -12x^2+9x \]

- nincompoop

alright, guy
what have you learned so far?

- nincompoop

have you learned derivative by limit definition yet?

- anonymous

no or maybe i did but i dont remember. can one of u show me step by step @UsukiDoll @nincompoop

- nincompoop

okay do you know what a derivative is first?

- anonymous

no @nincompoop

- nincompoop

ahhhhh

- nincompoop

do you know what a slope is?

- anonymous

once i have f(x)=-12x^2+9(x) what would i do?

- nincompoop

I can give you the general formula for power-rule, but it won't help you much in the long run if you have no clue what derivatives are.

- nincompoop

so do you know what is slope?

- nincompoop

I am asking a series of questions to see where is the proper place to begin.

- anonymous

no i dont @nincompoop

- Astrophysics

\[\frac{ d }{ dx } x^n = nx^{n-1}\] power rule

- nincompoop

man...

- nincompoop

laughing out loud

- UsukiDoll

wow nin... don't be rude -_-

- nincompoop

I'd use \(a \) instead of the coefficient n

- nincompoop

whatever floats floats

- anonymous

@UsukiDoll can u please help me

- nincompoop

alright, I think we've got a problem here
I am dumbfounded why you're doing derivative when you do not know what slopes are.

- nincompoop

in any case, we can go ahead and start with slope in general

- nincompoop

begin by our day-to-day language, slope pertains to the steepness of something
think of a slide or a hill or anything that goes down or up, it will have a slope

- nincompoop

now we can try to infuse a some math into the language

- Astrophysics

Well I don't think you have to go that far nin, I'm sure OP knows what slope is and just needs to remember |dw:1436327588479:dw| one image will do wonders

- nincompoop

I was just about to draw

- anonymous

okay i already know this?

- nincompoop

are you asking us or telling us?

- anonymous

telling u

- nincompoop

alright great!
now we can move on to derivatives! laughing out loud

- Astrophysics

But for your question, you find the derivative then plug in the value of x they've given you

- UsukiDoll

sorry I'm with another user right now.

- nincompoop

basically derivative pertains the slope at a particular instant

- nincompoop

|dw:1436327777742:dw|

- nincompoop

a good example of the instant that I am referring to is where one of the lines intersects at one point with the circle

- Astrophysics

Jessica were you taught definition\[f'(x) = \lim_{h \rightarrow 0} \frac{ f(x+h)-f(x) }{ h }\] of derivative, I think that's what you have to use

- nincompoop

now before we proceed, we must be able to identify and know about continuous functions

- nincompoop

think of this portion as an algebra recap
will you be able to tell us if the equation you're given is continuous or not?

- nincompoop

if you're unsure, now is the time to learn them
http://tutorial.math.lamar.edu/Classes/CalcI/CalcI.aspx

- nincompoop

review on tangents with pretty awesome illustration
http://tutorial.math.lamar.edu/Classes/CalcI/Tangents_Rates.aspx

- nincompoop

let us know when you've digested the concept of tangents and derivatives
because the next part will be testing your algebra skills with derivatives using limit-definition.

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