1、原式=(x-z)^2-(2y)^2-(x-z+y)^2
=(2x-2z+y)(-y)-4y^2
=-2xy+2yz-y^2-4y^2
=-2xy+2yz-5y^2
2、x=4/3 1/x=3/4
1/x^2-2/x+1=9/16-3/2+1=1/16
3、a+b=7
(a+b)^2=a^2+2ab+b^2=49
a^2-ab+b^2=49-3ab=49-3*12=13
4、3x^2-x-3=0 3x-1-3/x=0
3(x-1/x)=1 x-1/x=1/3
(x-1/x)^2=x^2-2+1/x^2=1/9
x^2+1/x^2=1/9+2=19/9
5、設(shè)x^2-4x+5=y
則x^2-4x+5-y=0
△=16-20+4y≥0
∴y≥1
即代數(shù)式x平方－4x+5的值≥1,最小值為1
6、由（x+2y)(x-2y)=－5(y平方－5分之6）
得x^2+y^2=25/6
由2乘以x乘以（y-1)+4(2分之1x－1）＝0
得xy=2
(1)(x-y)^2=x^2-2xy+y^2=25/6-2*2=1/6
(2)x^4+y^4-x^2y^2=(x^2+y^2)^2-3x^2y^2
=(25/6)^2-3*2^2
=625/36-12
=193/36