下列式子中,不成立的是(  )A.(x-y+z)(x-y-z)=(x-y)2-z2B.(x+y-z)(x-y-z)=x2-(y-z)2C.(x-y-z)(x+y

下列式子中,不成立的是(  )A.(x-y+z)(x-y-z)=(x-y)2-z2B.(x+y-z)(x-y-z)=x2-(y-z)2C.(x-y-z)(x+y

题型:单选题难度:简单来源:不详
下列式子中,不成立的是(  )
A.(x-y+z)(x-y-z)=(x-y)2-z2B.(x+y-z)(x-y-z)=x2-(y-z)2
C.(x-y-z)(x+y-z)=(x-z)2-y2D.(x-y-z)(x+y+z)=x2-(y+z)2
答案
A、(x-y+z)(x-y-z)=[(x-y)+z][(x-y)-z]=(x-y)2-z2,故正确;
B、(x+y-z)(x-y-z)=[(x-z)+y][(x-z)-y]=(x-z)2-y2,故错误;
C、(x-y-z)(x+y-z)=[(x-z)-y][(x-z)+y]=(x-z)2-y2,故正确;
D、(x-y-z)(x+y+z)=[x-(y+z)][x+(y+z)]=x2-(y+z)2,故正确.
故选B.
举一反三
已知(a+b+1)(a+b-1)=63,则a+b=______.
题型:填空题难度:一般| 查看答案
计算(3a-b)(-3a-b)等于(  )
A.9a2-6ab-b2B.-9a2-6ab-b2
C.b2-9a2D.9a2-b2
题型:单选题难度:一般| 查看答案
若a=
3a

,则(a+1)(a-1)=______.
题型:填空题难度:一般| 查看答案
计算:(-3x-2)(-3x+2)=______.
题型:填空题难度:一般| 查看答案
若x+y=1004,x-y=2,则代数式x2-y2的值是______.
题型:填空题难度:一般| 查看答案
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