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问题: 极限

lim(X→0)IncosAX/IncosBX
A≠0 B≠0

解答:

lim(X→0)[IncosAX/IncosBX]
= lim(X→0)[(IncosAX)'/(IncosBX)']
= lim(X→0)[(-A*sinAX/cosAX)/(-B*sinBX/cosBX)]
= (A/B)lim(X→0)[(sinAX/sinBX)]*lim(X→0)[(cosBX/cosAX)]
= (A/B)lim(X→0)[(sinAX)'/(sinBX)']*(1)
= (A/B)lim(X→0)[(A*cosAX)'/(B*cosBX)']
= (A/B)^2