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Understanding derivitaves

  1. Apr 4, 2008 #1
    I think I finally figured out derivitaves, but not sure...

    The derivative/differential of x in
    x is 1
    3x + 5 is 3
    5x^2 - 2 is 10

    And breaking down a quadratic thus

    3x^5 + 2x^3 + 5x - 1
    The first derivative is 15x^4 + 6x^2
    The second derivative is 60x^3 + 12x
    Third 180x^2
    Fourth 360x
    And final 360.
     
  2. jcsd
  3. Apr 4, 2008 #2
    No, first and third are wrong.

    1. 15x^4 + 6x^2 + 5
    2. 60x^3 + 12x
    3. 180x^2 + 12
    4. 360x
    5. 360
     
  4. Apr 4, 2008 #3
    The derivative of [tex]5x^2-2[/tex] is actually [tex]10x[/tex].
     
  5. Apr 4, 2008 #4
    Ah...That was the area I had a problem with...The final solitary number...
    Wado (thanks)
     
  6. Apr 4, 2008 #5

    HallsofIvy

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    The derivative (not differential) of 5x2- 2 at at x= 1 is 10. More generally, the derivative of 5x2- 2 at any x is 10x. The differential of x is dx, the differential fo 3x+ 5 is 3dx and the differential of 5x2- 2 is 10x dx.

    The first derivative is 15x4+ 6x2+ 5

    Well, I wouldn't call it "final". That's the fourth derivative. The fifth derivative, and all succeeding derivatives is 0.
     
  7. Apr 4, 2008 #6
    don't you mean the differential of y?

    isn't the differential of x : dx?
     
  8. Apr 5, 2008 #7
    I don't see any
    y's in there. It can be any variable expressed as a function of x.
    I think this is what Halls said also!
     
  9. Apr 5, 2008 #8
    woops
     
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