化简下列各式:(1)-(x+y)+(3x-7y);  
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化简下列各式:
(1)-(x+y)+(3x-7y); (2)(4a2-3b2)-[2(a2-1)+2b2-3]
(1)-(x+y)+(3x-7y); (2)(4a2-3b2)-[2(a2-1)+2b2-3]
(1)原式=-x-y+3x-7y,
=2x-8y;
(2)原式=4a2-3b2-[2a2-2+2b2-3],
=4a2-3b2-2a2+2-2b2+3,
=2a2-5b2+5.
=2x-8y;
(2)原式=4a2-3b2-[2a2-2+2b2-3],
=4a2-3b2-2a2+2-2b2+3,
=2a2-5b2+5.