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

User Paulo Oliveira
by
6.1k points

2 Answers

4 votes

Answer:A 945 is correct

Explanation:

User Maarten Derickx
by
6.4k points
5 votes
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
User Zhongyu Kuang
by
6.5k points
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