help out pls. Thanks

 Let f(x)=−x^4−6x^3+9x−1 Find the open intervals on which f is concave up (down). Then determine the x-coordinates of all inflection points of f

  • M F H M F H

    concave up/down means that the second derivative is positive or negative. So you just have to study the sign of the 2nd derivative. The inflection points are those where the sign changes.

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