如图所示
(1)
lim((x,y)->(0,1)) ( 1-xy)/(x^2+y^2)
=(1-0)/(1+0)
=1
(2)
a=(3,-1,2)
|a| =√(3^2+1^2+2^2) =√14
(3)
lim((x,y)->(0,0)) [ 2-√(xy+4) ] /(xy)
=lim((x,y)->(0,0)) [ 4-(xy+4) ] /{ (xy).[ 2+√(xy+4) ] }
=lim((x,y)->(0,0)) -1 /[ 2+√(xy+4) ]
=-1/( 2+ 2)
=-1/4
(4)
a=(1,-2,3) , b=(3,1,-2)
a.b
=(1,-2,3) .(3,1,-2)
=3-2 -6
=-5
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