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a
increasing on [0,∞)
b
decreasing on [0,∞)
c
increasing on [0,π/e) and decreasing on [π/e,∞)
d
decreasing on [0,π/e,) and increasing on [π/e,∞)
answer is B.
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Detailed Solution
Since ex2 increases on [0,∞) so it is enough to consider f(x)=log(π+x)log(e+x)f′(x)=log(e+x)×1π+x−log(π+x)1e+x(log(e+x))2=f′(x)=log(e+x)×(e+x)−(π+x)log(π+x)(π+x)(e+x)(log(e+x))2Since log function is an increasing function and e<π,log(e+x)0 Thus f′(x)<0 for ∀x>0⇒f(x) decreases on (0,∞)