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Math Graphing

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x^3 < 3x^2

would become x(x^2-3x)

then how would I graph this?

  • Math Graphing -

    x(x^2-3x) < 0
    x^2(x-3) < 0

    critical values of x=0 , x=3

    on a number line, mark x=0 and x=3, splitting the line into 3 parts

    1. x<0
    pick any number < 0, say x=-5
    (+)(-) < 0 , that's what we want

    2. 0 < x < 3 , pick a value, let's pick x = 1
    (+)(-) < 0 , good !

    3. x> 3, let x=5
    (+)(+) > 0 , no good

    so x < 3 will work.

    another way is know what a general cubic looks like
    you would have
    y = x^2(x-3)
    there would be double root at x=0, so it touches at x=0 without crossing, and it crosses at x = 3
    easy to sketch, one can see that the curve is below the x-axis for x< 0 as well as between 0 and 3.
    so that is our domain, namely x < 3

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