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

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24 February, 15:40

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

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Answers (2)

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Izabelle Morales · Answer 1

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

Messiah · Answer 2

Answer:A 945 is correct