ab互为相反数,
a+b=0
cd互为倒数,
cd=1
x的绝对值等于1
x=1或-1
所以
-(a+b+cd)x-cd
=-（0+1）×1-1
=-1-1
=-2
或
-(a+b+cd)x-cd
=-（0+1）×（-1）-1
=1-1
=0