丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值

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丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值丨x丨=3,x=±3

丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值
丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值

丨x丨=3,丨y丨=5,且丨x+y丨=-x-y,求x-y的值
丨x丨=3,x=±3
丨y丨=5,y=±5
丨x+y丨=-x-y = -(x+y)
∴x+y<0
∴x=±3,y=-5
∴x-y = ±3-(-5) = 2,或8

丨x+y丨=-x-y 则有:x+y<0
所以可得:x=3 或-3
y=-5
所以:当x=3,y=-5时,x-y=8
当x=-3,y=-5时,x-y=2

8或2

丨x丨=3,x1=3,x2=-3;
丨y丨=5,y1=5,y2=-5;
丨x+y丨=-x-y=-(x+y),
x+y<0,
x1+y2=3-5=-2,x-y=3-(-5)=8;
或x2+y2=-3-5=-8,x-y=-3-(-5)=2;