(2)
令1/x=tï¼åx=1/t
xââï¼åtâ0
åå¼=lim (-sint+tcost)cost/[(e^(t+a)-e^a)²sint]
tâ0
=lim -(sint-tcost)cost/[e^(2a)·(e^t -1)²sint]
tâ0
=lim -(t-tcost)cost/[e^(2a)·t²Â·t]
tâ0
=lim -t·½t²Â·1/[e^(2a)·t³]
tâ0
=lim -½t³/[e^(2a)·t³]
tâ0
=lim -½/e^(2a)
tâ0
=-1/[2e^(2a)]
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