当X→π/4时,(tanX-1)/(sin4X)是0/0型极限,可采用罗毕达法则对分母分子各微分一次.得:
lim(tanX-1)/(sin4X)=lim[sec²X/(4cosX)]
当X→π/4时,sec²X=2,4cosX=2√2.代入上式得:
lim(tanX-1)/(sin4X)=2/(2√2)=1/√2
(注:是X→π/4,不是X→X/4)
当X→π/4时,(tanX-1)/(sin4X)是0/0型极限,可采用罗毕达法则对分母分子各微分一次.得:
lim(tanX-1)/(sin4X)=lim[sec²X/(4cosX)]
当X→π/4时,sec²X=2,4cosX=2√2.代入上式得:
lim(tanX-1)/(sin4X)=2/(2√2)=1/√2
(注:是X→π/4,不是X→X/4)