Which best describes the relationship between the successive terms in the sequence shown?

9, –1, –11, –21, …

a)the common difference is –10.
b)the common difference is 10.
c)the common ratio is –9.
d)the common ratio is 9.

i believe i understand it but have to ask it would be the common difference is -10 bevause you would take -1-9 and get -10? ,

You almost got it. Be careful with how the question is worded. A "common difference" between these sequential numbers already indicates subtraction. So you have to answer with what number is being subtracted from each number in order to equal the next. 9 - 10 is -1. Next, -1 - 10 is -11. Thus, the common difference between successive terms here is 10. Next, the difference between -11 and -21 is 10. You could continue the sequence: -21 - 10 = -31 and so on.