由a+b+2的绝对值与[2ab-1]的4次方互为相反数 可知
a+b+2=0 2ab-1=0
解得a+b=-2 ab=1/2
a+b/3ab-(3ab+1)/(a+b)=-2/(3x1/2)-(3x1/2+1)/-2
=-2x2/3+(3/2+1)x1/2
=-4/3+3/4+1/2
=-1/12