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Math Help - First Principles... 1/x^2 really can't do this...

  1. #1
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    First Principles... 1/x^2 really can't do this...

    Differentiate 1/x^2 from first principles..
    Would love someone to help me with this!
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  2. #2
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    What do you mean by "first principles"? Do you mean the limit definition of the derivative? Or from using basic derivative theorems? Or what?
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  3. #3
    Behold, the power of SARDINES!
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    Quote Originally Posted by Snaggle View Post
    Differentiate 1/x^2 from first principles..
    Would love someone to help me with this!
    What have you tried?

    The defintion is

    f'(x)=\lim_{h \to 0}\frac{f(x+h)-f(x)}{h}
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  4. #4
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    \frac{\frac{1}{(x+ h)^2}- \frac{1}{x^2}}{h}= \frac{\frac{x^2}{x^2(x+h)^2}- \frac{(x+h)^2}{x^2(x+h)^2}}{h}
    = \frac{x^2- (x+h)^2}{hx^2(x+ h)^2}

    You should be able to now reduce that to something that has a limit as x goes to 0.

    Okay, the first post I did this morning, I used "tex" and it didn't work so I went back to "math" and that did work. "Great" I thought- they have that fixed now. But on this post I used "math" and it didn't work- I had to use "tex". What is going on?
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