a与2b互为倒数,-c与d/2互为相反数
a*2b=1 -c+d/2=0
2ab-2c+d-2x/3
=1+2(-c+d/2)-2x/3
=1+2*0-2x/3
=1-2x/3
当x=3时原式=1-2=-1
当x=-3时原式=1+2=3