设函数f(x)=x^3-3x^2

1个回答

  • 解由g(x)=e^x*f(x)

    =e^x*(x³-3x²)

    求导函数

    g'(x)=[e^x*(x³-3x²)]'

    =(e^x)'(x³-3x²)+(e^x)(x³-3x²)'

    =(e^x)(x³-3x²)+(e^x)(3x²-6x)

    =(e^x)(x³-6x)

    =(e^x)(x²-6)x

    =(e^x)(x-√6)(x+√6)x

    令g'(x)=0

    解得x=√6或x=-√6或x=0

    当x属于(√6,正无穷大),f'(x)>0

    当x属于(0,√6),f'(x)<0

    当x属于(-√6,0),f'(x)>0

    当x属于(负无穷大,-√6),f'(x)<0

    即函数g(x)=e^x*f(x)的单调增区间(√6,正无穷大)和(-√6,0).

    函数g(x)=e^x*f(x)的单调减区间(0,√6)和(负无穷大,-√6).