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=

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