lim(x→0)(x2-sin2x)/x^4 =lim(x→0)(x+sinx)(x-sinx)/x^4 =lim(x→0)(x+sinx)x3/6x^4 =1/6*lim(x→0)(x+sinx)/x =1/6*(1+1) =1/3 lim(x→0)(x2-sin2x)/x^4 =lim(x→0)(2x-2sinxcosx)/4x3 =lim(x→0)(2x-sin2x)/4x3 =lim(x→0)(2-2cos2x)/12x2 =lim(x→0)(1-cos2x)/6x2 =lim(x→0)2sin2x/12x =lim(x→0)2cos2x/6 =1/3 等价替换也好洛必达法则也好都是1/3,你是怎麼算错的?
因为分子是相减的形式，不能用等价无穷小代换
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