实数ab互为相反数,a+b=0
cd互为倒数,cd=1
x的绝对值为根号7,x=±√7,x^2=7
x的平方+(a+b+cd)x+根号a+b+cd的立方根
=7+(0+1)x+√0+1的立方根
=8+x
=8±√7