若x+y=8,x²-y²=48,则y-x=

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若x+y=8,x²-y²=48,则y-x=若x+y=8,x²-y²=48,则y-x=若x+y=8,x²-y²=48,则y-x=y-x=-(x

若x+y=8,x²-y²=48,则y-x=
若x+y=8,x²-y²=48,则y-x=

若x+y=8,x²-y²=48,则y-x=
y-x
=-(x²-y²)÷(x+y)
=-48÷8
=-6


x²-y²=48
<=>(x+y)(x-y)=48
<=>8(x-y)=48
<=>8x-8y=48
<=>y-x=-6

这样做比较清楚
x²-y²=48
则(x+y)(x-y)=48
将x+y=8代人得
8(x-y)=48
x-y=6
所以y-x=-6