Question

Find the derivative of f(x) = -12x2 + 9x at x = 6.

-112.5
-135
-90
-108
@ganeshie8 @hero @dan815 @perl @pooja195 @nincompoop @CGGURUMANJUNATH @zepedrix @usukidoll

Answer 1

use power rule

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

alright, guy
what have you learned so far?

Answer 6

have you learned derivative by limit definition yet?

Answer 7

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

Answer 8

okay do you know what a derivative is first?

Answer 9

no @nincompoop

Answer 10

ahhhhh

Answer 11

do you know what a slope is?

Answer 12

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

Answer 13

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.

Answer 14

so do you know what is slope?

Answer 15

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

Answer 16

no i dont @nincompoop

Answer 17

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

Answer 18

man...

Answer 19

laughing out loud

Answer 20

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

Answer 21

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

Answer 22

whatever floats floats

Answer 23

@UsukiDoll can u please help me

Answer 24

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.

Answer 25

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

Answer 26

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

Answer 27

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

Answer 28

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 one image will do wonders

Answer 29

I was just about to draw

Answer 30

okay i already know this?

Answer 31

are you asking us or telling us?

Answer 32

telling u

Answer 33

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

Answer 34

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

Answer 35

sorry I'm with another user right now.

Answer 36

basically derivative pertains the slope at a particular instant

Answer 37

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

Answer 38

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

Answer 39

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

Answer 40

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?

Answer 41

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

Answer 42

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

Answer 43

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.