问一下下面两个多元函数的极限求值lim=(x²-y²-2x+2y)/(x+ y-2) ① (x,y)→(2,0) ②(x,y)→(0,2)

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问一下下面两个多元函数的极限求值lim=(x²-y²-2x+2y)/(x+ y-2) ① (x,y)→(2,0) ②(x,y)→(0,2)
问一下下面两个多元函数的极限求值
lim=(x²-y²-2x+2y)/(x+ y-2) ① (x,y)→(2,0) ②(x,y)→(0,2)

问一下下面两个多元函数的极限求值lim=(x²-y²-2x+2y)/(x+ y-2) ① (x,y)→(2,0) ②(x,y)→(0,2)
将分子因式分解,和分母约掉公因数即可
lim(x,y)→(2,0) (x²-y²-2x+2y) / (x+y-2)
= lim (x²+xy-2x -xy-y²+2y) / (x+y-2)
= lim [x(x+y-2)-y(x+y-2)] / (x+y-2)
= lim [(x-y)(x+y-2)] / (x+y-2)
= lim (x-y)
= 2 - 0
= 2
lim(x,y)→(0,2) (x²-y²-2x+2y) / (x+y-2)
= lim (x-y)
= 0 - 2
= -2