求极限,实话说是高数题,求学霸帮忙咯,谢谢.

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求极限,实话说是高数题,求学霸帮忙咯,谢谢.
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求极限,实话说是高数题,求学霸帮忙咯,谢谢.
求极限,实话说是高数题,求学霸帮忙咯,谢谢.

 


求极限,实话说是高数题,求学霸帮忙咯,谢谢.
令t=x^2+y^2,则t→0,
原式=limt→0 (1-cost)/tln(1+t),
=limt→0 2sin^2(t/2)/t*t,(ln(1+t)~t,替换)
=limt→0 2*(t/2)^2/t^2,(sint/2~t/2,替换)
=1/2.