Find the sum of the first 21 terms of the sequence 5, 9, 13, 17, 21, ... a. 945 c. 947 b. 944 d. 946

Question

Mathematics

Kirsten Becker

10 March, 07:38

Find the sum of the first 21 terms of the sequence 5, 9, 13, 17, 21, ... a. 945 c. 947 b. 944 d. 946

+4

Answers (2)

Know the Answer?

Avah Sanders · Answer 1

Answer:A 945 is correct

Julius Quinn · Answer 2

See how the arithmetic sequence is made:

5, 5+4=9, 9+4=13, 13+4=17, ...

So the 21th term will be:

5 (first term) + 20 (n-1 term) •4 = 85

And the sum of the first 21 is:

21 (5+85) / 2 = 21•45 = 945