a与2b互为负倒数,则a×2b=2ab=-1
-c与d/2互为相反数,则 -c+d/2=(-2c+d)/2=0,-2c+d=0
m与n互为相反数,则m=-n,m÷n=-1
2ab-2c+d+m÷n
=-1+0+(-1)
=-2