|x+y|

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|x+y||x+y|似乎要画图这图怎么画求思路|x+y|充分性：特殊法令x=1.9y=0.01显然不成立必要性：|x+y|

|x+y|
|x+y|<2是|x|<1且|y|<1的什么条件
似乎要画图这图怎么画求思路

|x+y|
充分性：特殊法令x=1.9 y=0.01 显然不成立
必要性：|x+y|

{(x,y) |x|+|y| x>y?x:y x^/y-x-y^/y-x化简. 化简x(y-x)-y(x-y) 行列式计算 x y x+y y x+y x x+y x y|x y x+y ||y x+y x ||x+y x y | y/(x+y)-x/(x-y) x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x y x+yy x+y xx+y x y (3x-y)(3y+x)-(x-y)(x+y) 化简x/y(x+y)-y/x(x+y) 化简 x / y(x+y) - y / x(x+y) = 化简:(x+ y)(x-y) +(x+ y) +(x-y) x+y (x+y) |x+y| x y x+yy x+y xx+y x y 化简y(x+y)+(x+y)(x-y)-x^2 |x|+|y|