What is the general term equation, a_n , for the arithmetic sequence 5, 1,–3, –7…and what is the 21st term of this sequence? hint: a_n=a_1+d(n-1), where a_1 is the first term and d is the common difference

The difference between each term is -4, so we know that part of the general term is -4n. Now we need to adjust -4n so at u1 it is 5. Therefore -4+x=5 and we rearrange to see x is 9.

Therefore our general sequence is:


Now we can substitute easily into the second equation with the common difference of 4:

Ithink your answer is c hope that