a+b=0;-->a=-b;
ac=1;
bc=-1;
x=±2;
当x=2;
=4-3a+1/2-3b+(-1)^2011
=4-3(a+b)+1/2-1
=3.5;
x=-2时;
=4-3a-1/2-3b+(-1)^2011
=4-3(a+b)-1/2-1
=2.5;
a+b=0;-->a=-b;
ac=1;
bc=-1;
x=±2;
当x=2;
=4-3a+1/2-3b+(-1)^2011
=4-3(a+b)+1/2-1
=3.5;
x=-2时;
=4-3a-1/2-3b+(-1)^2011
=4-3(a+b)-1/2-1
=2.5;