Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: How do you differentiate this

  1. Mar 20, 2007 #1
    x^2y

    the y is biglike the x its not small

    and how do you differentiate this
    xy^2

    for the first one i used the product rule and thesecond one and i get a different answer then what i was suppost to get
     
  2. jcsd
  3. Mar 20, 2007 #2
    for the first one i didthis

    x^2 d/dx y dy/dx + y d/dx x^2

    x^2 y' + y+ 2x

    so how come im not getting 2x 2y
     
  4. Mar 20, 2007 #3
    :confused: You need an equation, not an expression, i.e. [tex]x^{2}y = ?[/tex]. Also, are you familiar with implicit differentiation?
     
    Last edited: Mar 20, 2007
  5. Mar 20, 2007 #4
    ill give u the equation x^3+x^2y+4y^2=6
     
  6. Mar 20, 2007 #5
    i understand it now, the answer of this was factored out or cleaned up a bit, so i didn't notice there was an x outside of the paranthesis of 2y
     
  7. Mar 20, 2007 #6
    [tex]x^3 + x^2y + 4y^2 = 6[/tex]

    Okay, but do you know what implicit differentiation is? For example,

    [tex]x + y = 1 [/itex]

    [tex]\frac{dx}{dx} + \frac{dy}{dx} = \frac{d1}{dx} [/tex]

    [tex]1 + \frac{dy}{dx} = 0 [/tex]

    Also for a product, the product rule applies, e.g.

    [tex]xy = 1[/tex]

    [tex]x*\frac{dy}{dx} + \frac{dx}{dx}*y = 0 [/tex]
     
    Last edited: Mar 20, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook