limx趋近于0时，sin(sinx）/x的极限

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sin(sinx)~sinx~x (x->0) (等价无穷小)
原式=lim{x->0}x/x=1

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运用等价无穷小代简做孙换
x→0,sinx~x
lim（胡余x→0）sin(sinx）/x
＝lim（拦链x→0）sinx/x
＝1

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