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幼苗
共回答了14个问题采纳率:92.9% 举报
(1)
f′(x)=1/x-(b+2)/(x+1)²=(x²-bx+1)/(x(x+1)²)
令h(x)=1/(x(x+1)²),a=b
则f(x)具有性质P(a)
(2)
△=b²-4
∴当b∈(-2,2]时
f(x)在(1,+∞)上单调增
当b∈(-∞,-2]时
f(x)在(1,+∞)上单调增
当b∈(2,+∞)时
f(x)在(1,(b+sqr(b²-4))/2)上单调减,在((b+sqr(b²-4))/2,+∞)上单调增
综上:
当b∈(-∞,2]时
f(x)在(1,+∞)上单调增
当b∈(2,+∞)时
f(x)在(1,(b+sqr(b²-4))/2)上单调减,在((b+sqr(b²-4))/2,+∞)上单调增
1年前
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