1.3a2+（4a2-2a-1)-2(3a2-a+1),其中a =负二分之一
=3a²+4a²-2a-1-6a²+2a-2
=a²-3
=(-1/2)²-3
=1/4-3
=0.25-3
=-2.75
2.n+【4m-3（m-2n）-4n】,其中m=2,n=负二分之三
=n+4m-3m+6n-4n
=m+3n
=2+3*(-3/2)
=2-9/2
=2-4.5
=-2.5
3.已知x+4y=-1,xy=5,求（6xy+7y）+【8x-（5xy-y+6x）】的值
（6xy+7y）+【8x-（5xy-y+6x）】
=6xy+7y+8x-5xy+y-6x
=xy+8y+2x
=xy+2*(x+4y)
=5+2*(-1)
=5-2
=3