a.b互为相反数,a+b=0
c.d互为倒数,c×d=1
x的绝对值等于2,x=±2
①x=2时
3x-(a+b+c×d)x
=3*2-(0+1)*2
=6-2
=4
②x= -2时
3x-(a+b+c×d)x
=3*(-2)-(0+1)*(-2)
= -6+2
= -4