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Math Help - Find the points of inflection and discuss the concavity of the graph of the function.

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    Find the points of inflection and discuss the concavity of the graph of the function.

    so here's the function
    f(x) = 2sinx + sin2x and in order to find the concavity i need to find the second derivative which is this.... f ''(x)= -2sinx - 4sin2x.... now how do i find the critical numbers to determine the concavity of the function? how to i set x equal to zero to find the critical numbers.... please help!!
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  2. #2
    MHF Contributor MarkFL's Avatar
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    Re: Find the points of inflection and discuss the concavity of the graph of the funct

    Equating the second derivative to zero, we find:

    -2(\sin(x)+2\sin(2x))=0

    \sin(x)+2\sin(2x)=0

    Now, use the double-angle identity for sine, then factor. What do you find?
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