已知x+y=3,xy=-10,求（1）x平方-xy+y平方；（2）|x-y|

已知x+y=3,xy=-10,求（1）x平方-xy+y平方；（2）|x-y|
已知x+y=3,xy=-10,求（1）x平方-xy+y平方；（2）|x-y|

已知x+y=3,xy=-10,求（1）x平方-xy+y平方；（2）|x-y|
x+y=3
(x+y)²=9
x²+y²+2xy=9
x²+y²-20=9
x²+y²=29
x平方-xy+y平方
=29-（-10）
=39
(x-y)²
=x²+y²-2xy
=29-2(-10)
=49
Ix-yI
=√(x-y)²
=√49
=7

x+y=3
(x+y)^2=9
x^2+y^2+2xy=9
x^2-xy+y^2+3xy=9
x^2-xy+y^2+3*(-10)=9
x^2-xy+y^2-30=9
x^2-xy+y^2=39
(x-y)^2
=(x+y)^2-4xy
=3^2-4*(-10)
=9+40
=49
x-y=±7
|x-y|=7

1.x^2-xy+y^2
=(x+y)^2-3xy
=3^3-3×(-10)
=39
2.|x-y|=√(x-y)^2
=√[(x+y)^2-4xy]
=√[3^2-4×(-10)]
=√49=7