A:+1
B:+2
C:+3
D:+4
定义:a是不为1的有理数,我们把 11−a 称为a的差倒数.
如:2的差倒数是 11−2=−1 ,﹣1的差倒数是 11−(−1) = 12 .
已知 a1=−13 ,
— ______. I have to do my homework.
— _____ you at school last night?
— No, I _____ at home.