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  • 設(shè)m為實(shí)數(shù),函數(shù)f(x)=2x^2+(x-m)|x-m|,h(x)=f(x)/x x不等于0 0x=0 (1)若f(1)>=4,求m的取值范圍(2)

    設(shè)m為實(shí)數(shù),函數(shù)f(x)=2x^2+(x-m)|x-m|,h(x)=f(x)/x x不等于0 0x=0 (1)若f(1)>=4,求m的取值范圍(2)
    當(dāng)m>0時,求證h(x)在[m,+∞)上是單調(diào)遞增函數(shù)
    數(shù)學(xué)人氣:615 ℃時間:2020-09-30 22:44:06
    優(yōu)質(zhì)解答
    (1)
    f(1)=2+(1-m)|1-m| ≥ 4
    當(dāng)m>1時,(1-m)(m-1) ≥ 2,無解;
    當(dāng)m ≤ 1時,(1-m)(1-m) ≥ 2,解得:m ≤ 1-√2
    ∴m的取值范圍是:m ≤ 1-√2
    (2)
    ∵m>0,x ≥ m
    ∴h(x)=f(x)/x
    =[2x²+(x-m)(x-m)]/x
    =[2x²+x²+m²-2mx]/x
    =(3x²+m²-2mx)/x
    =3x+(m²/x)-2m
    任取m ≤ x1 ≤ x2,
    則h(x2)-h(huán)(x1)
    =[3x2+(m²/x2)-2m]-[3x1+(m²/x1)-2m]
    =(3x2-3x1)+[ m²(x1-x2) /(x1x2) ]
    =[3x1x2(x2-x1)+m²(x1-x2)]/(x1x2)
    =[(x2-x1)(3x1x2-m²)]/(x1x2)
    =(x2-x1)[(3x1x2-m²)/(x1x2)]
    ∵x2-x1>0,3x1x2-m²>3m²-m²>0,x1x2>0
    ∴h(x2)-h(huán)(x1)>0
    即h(x1)<h(x2)
    即h(x)在[m,+∞)為單調(diào)遞增函數(shù)
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