a,b互为倒数,c,d互为相反数
ab=1,c+d=0
ab+c+d/2m-3m=1+0/2m-3m=1-3m
丨m丨=2
m=2 时,ab+c+d/2m-3m=1-3*2=-5
m=-2 时,ab+c+d/2m-3m=1-3*(-2)=7