é常令y=kx(æ¹å)æx^n or 缩æ¾
1
y^2=z
xz/(x^2+z^2)
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2
|xy^2/(x^2+y^2)|<=|xy^2/(y^2)|<=|x| ->0
4
|xy^3/(x^2+y^2)|<=|xy^3/(y^2)|<=|xy| ->0
3
令x=yï¼æé=1/2
令x=2y, æé=2/5
令y=3x, æé=3/10
x=0 or y=0, æé=0
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