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Relation of the graph of a function with the graph of it's derivative

  1. Jan 17, 2010 #1
    What is the relation between the graph of a function and the graph of it's derivative?

    Suppose that the function is x^2. It's derivative is 2x. If we graph both x^2 and 2x on the same coordinate axes, can we conclude anything about x^2 by looking at the graph of 2x, or vice versa (i.e. can we conclude anything about 2x by looking at the graph of x^2)?

    For example, can we tell what will be the slope of the tangent line at a curve at x^2 by looking at the graph of it's derivative 2x?

    If there is no relation between the two, then what is the use of graphing the derivative of a function?
     
  2. jcsd
  3. Jan 17, 2010 #2
    You ought to be able to tell where it it is increasing, decreasing, concave up, concave down, where it has maxima or minima or inflection points just by looking at the sign of the first derivative and where it's increasing or decreasing.
     
  4. Jan 18, 2010 #3
    I'm not talking about when you find the slope of the tangent at some point by substituting the point into the the equation of the derivative. I'm talking about the equation of the derivative itself (such as y=2x for y=x^2).

    I mean: what can we find out about x^2 just from the equation 2x (or it's graph) (without substituting any values)?
     
  5. Jan 18, 2010 #4
    Exactly what I said.
     
  6. Jan 21, 2010 #5
    Oops.. I think I'm asking the question the wrong way. My question is that by looking at the plot of 2x (which is a straight line), what can we say about the x^2 (which is a curve), without knowing that the straight line's equation is 2x and the curve's equation is x^2?
     
  7. Jan 24, 2010 #6
    Again, exactly what I said.
     
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