已知a,b互为相反数,c,d互为倒数,若a不等于0,
a+b=0 b/a=-1
cd=1
3a+3b+a分之b+2分之1 cd
=3(a+b)+b/a+1/2*cd
=3*0-1+1/2*1
=-1+1/2
=-0.5