原式=lim(x->π/2) (sinx/cosx)/(sin5x/cos5x)
=lim(x->π/2) (sinπ/2/cosx)/(sin5π/2/cos5x)
=lim(x->π/2) (cos5x/cosx)
=lim(x->π/2) (-5sin5x/(-sinx))
=5
tan求导太麻烦
这么改一下：
=lim (sinx/cosx) /(sin5x/cos5x)
=limcos5x/cosx *sinx/sin5x
=limcos5x/cosx
洛必达
=lim5sin5x/sinx
=5
答案是1/5吗？
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