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(________)-(x2+xy)=2xy-y2.
y2-my-ab=(y-a)(y+b),则m应为
A.a+b
B.a-b
C.b-a
D.-a-b
(________)-(x2+xy)=2xy-y2.(按顺序去括号)
若+(2x+y)2=0,则x2-xy+y2的值是
A.7
B.5
C.1
D.3
若y2+4y+4+=0,则xy的值等于( ).
A.-6
B.-2
C.2
D.6