2-4a²-7a²-7ab-6等于多少,

2-4a²-7a²-7ab-6等于多少,

2-4a²-7a²-7ab-6
=（-4-7）a²-7ab+(2-6)
=-11a²-7ab-4

原式=(-4-7)a²-7ab+(2-6)
=-11a²-7ab-4

8丨x+1/2丨+丨x+1/2y+1丨=0
所以x+1/2=0
x+1/2y+1=0
x=-1/2
y=-2(x+1)=-1
所以原式=1/8+1/2=5/8
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