## anonymous one year ago 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

1. nincompoop

use power rule

2. anonymous

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

3. nincompoop

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

4. UsukiDoll

$f(x) = -12x^2+9x$

5. nincompoop

alright, guy what have you learned so far?

6. nincompoop

have you learned derivative by limit definition yet?

7. anonymous

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

8. nincompoop

okay do you know what a derivative is first?

9. anonymous

no @nincompoop

10. nincompoop

ahhhhh

11. nincompoop

do you know what a slope is?

12. anonymous

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

13. 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.

14. nincompoop

so do you know what is slope?

15. nincompoop

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

16. anonymous

no i dont @nincompoop

17. Astrophysics

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

18. nincompoop

man...

19. nincompoop

laughing out loud

20. UsukiDoll

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

21. nincompoop

I'd use $$a$$ instead of the coefficient n

22. nincompoop

whatever floats floats

23. anonymous

24. 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.

25. nincompoop

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

26. 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

27. nincompoop

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

28. 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

29. nincompoop

I was just about to draw

30. anonymous

okay i already know this?

31. nincompoop

are you asking us or telling us?

32. anonymous

telling u

33. nincompoop

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

34. Astrophysics

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

35. UsukiDoll

sorry I'm with another user right now.

36. nincompoop

basically derivative pertains the slope at a particular instant

37. nincompoop

|dw:1436327777742:dw|

38. 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

39. 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

40. nincompoop

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

41. 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?

42. nincompoop

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

43. nincompoop

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

44. 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.