(x-0.5y-1)(x-0.5y+1)-(x-0.5y-1)^2
=[(x-0.5y)-1][(x-0.5y)+1]-[(x-0.5y)-1]^2
=(x-0.5y)^2-1-[(x-0.5y)^2-2(x-0.5y)+1]
=-2+2(x-0.5y)
=2(x-0.5y-1)
=2[2.5-0.5*(-1.5)-1]
=2*2.25
=4.5
(x-0.5y-1)(x-0.5y+1)-(x-0.5y-1)^2
=(x-0.5y-1)（x-0.5y+1-x+0.5y+1)
=2(x-0.5y-1)
=2x-y-2
=4.5
上面的做得是对的
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