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[主观题]
已知f(x,y)=x2-y2-x+y+1.则f(x,y)=1. (1)x=y. (2)x+y=1.A.条件(1)充分,但条件(2)不充
已知f(x,y)=x2-y2-x+y+1.则f(x,y)=1. (1)x=y. (2)x+y=1.
A.条件(1)充分,但条件(2)不充分.
B.条件(2)充分,但条件(1)不充分.
C.条件(1)和条件(2)单独都不充分,但条件(1)和条件(2)联合起来充分.
D.条件(1)充分,条件(2)也充分.
E.条件(1)和条件(2)单独都不充分,条件(1)和条件(2)联合起来也不充分.
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