求lim(x-x*cosx)/(x-sinx)

来源:学生作业帮助网 编辑:六六作业网 时间:2024/05/14 05:41:11
求lim(x-x*cosx)/(x-sinx)求lim(x-x*cosx)/(x-sinx)求lim(x-x*cosx)/(x-sinx)x-xcosx=x(1-cosx),1-cosx与x^2/2等

求lim(x-x*cosx)/(x-sinx)
求lim(x-x*cosx)/(x-sinx)

求lim(x-x*cosx)/(x-sinx)
x-xcosx=x(1-cosx),1-cosx与x^2/2等价,所以,
lim(x→0)(x-xcosx)/(x-sinx)
=lim(x→0)(1/2×x^3)/(x-sinx) 使用洛必达法则
=lim(x→0)(1/2×3x^2)/(1-cosx)
=lim(x→0)(1/2×3x^2)/(1/2×x^2)
=3

用泰勒公式将cosx 和 sinx展开,取前两项
上面=x-x(1-x^2/2+o(x^3))=x^3/2
下面=x-(x-x^3/3!+o(x^3))=x^3/6
两式相除等于3