实数a、b互为相反数，c、d互为倒数x的绝对值为根号七则a+b=0cd=|x|=√7则√(a+b)=0x^2=|x|^2=√7^2=7则x^2+(a+b+cd)x+（根号a+b）+三次根号cd=7+x+1=8+x=8±√7
