老胖和小胖
幼苗
共回答了19个问题采纳率:84.2% 举报
2ln(x + 1) + b = x + 1
g(x) = 2ln(x + 1) - x + b - 1
g'(x) = 2/(x + 1) - 1 = 0
x = 1
-1 < x < 1:g'(x) > 0
x > 1:g'(x) < 0
g(1)为极大值,方程在[0,2]有两个实根,只须g(1) > 0 且g(0),g(2)均 0,b > 2(1 - ln2) (1)
g(0) = b - 1 < 0,b < 1 (ii)
g(2) = 2ln3 - 3 + b < 0,b < 3 - 2ln3 (iii)
(ii)(iii)结合得b < 3 - 2ln3
再与(i)结合得2(1 - ln2) < b < 3 - 2ln3
1年前
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老胖和小胖
对, 答案是2(1 - ln2) < b < 3 - 2ln3