若A,B互为倒数,c,d互为相反数,求2c+2d-3ab
问题描述：
若A,B互为倒数,c,d互为相反数,求2c+2d-3ab
答
-3
答
A,B互为倒数，ab=1
c,d互为相反数，c+d=0
故2c+2d-3ab=-3
答
A,B互为倒数,则A*B=1
C,D互为相反数,则C+D=0
2c+2d-3ab
=2(c+d)-3a*b
=2*0-3*1
=0-3
=-3