How could it be shown that limx→0[xln(ex+1ex−1)]=limx→∞[xln(ex+1ex−1)]=0?
Note that when x=0, we have x=0 (obviously) and ln(ex+1ex−1)=ln(20) which is indeterminate and when x→∞, we have x→∞ (obviously) and ln(ex+1ex−1)=ln(1+2ex−1)→ln1=0. So it is not possible to just multiply both.
I can't see L'Hopital working as the fraction in ln expands to a sum, not a fraction.
Here's a plot of the function in Desmos.
Any approaches?
Answer
xln(ex+1ex−1)=xln(ex+1)−xln(ex−1) and it is clear that xln(ex+1)→0 as x→0. To find the limit of xln(ex−1) apply L'Hopital Rule to ln(ex−1)1/x and use the fact that x2ex−1→0 as x→0 (by Another application of L'Hopital Rule). For limit as x→∞ use the fact that ln(ex+1)(ex−1)=ln(1+2ex−1) and then use the fact that ln(1+x) behaves like x as x→0.
No comments:
Post a Comment