a,b互为相反数,c,d互为倒数,x的绝对值等于1,
a+b=0,cd=1 x=1,或x=-1
x^2=1
-(a+b+cd)x-cd=-x-1
x=1,=> =-2
x=-1 => =0
x^2-(a+b+cd)x-cd=1-cdx-1=-x
=1,或-1