Find sn for the given arithmetic series.
a1 = 22, d = –8, n = 21

37,191

Step-by-step explanation:

You would first use the arithmetic sequence, which is a_n=a_1+(n-1)(d). Since you already have your a1, d, and n figured out, all you need to do is find the a_n. So, you would plug in your values. You should get -3520 as your answer for this equation, or in this case a_n=-3520. The reason why it's negative is because your common difference was negative.

Next, you would use the equation Sn=n(a1+an)/2. You already have all of your variables solved, so now you just plug everything in. As the answer, you should get -1749. Make sure you do not subtract -3520. What I mean by this is don't make the negative a subtraction sign. Add the negative to the 22. Otherwise, you will get it wrong.

Hope this helps!