SOLUTION: what is the sum of the arethmtic sequence below 2+5+8+..+59

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Question 890044: what is the sum of the arethmtic sequence below
2+5+8+..+59
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
First we determine how many terms, n.

a%5Bn%5D%22%22=%22%22a%5B1%5D%2B%28n-1%29d

where a%5B1%5D=2, a%5Bn%5D=59, d=5-2=8-5=3, 

59%22%22=%22%222%2B%28n-1%293

59%22%22=%22%222%2B3n-3

59%22%22=%22%223n-1

60%22%22=%22%223n

20%22%22=%22%22n

Now we use the sum formula:

S%5Bn%5D%22%22=%22%22expr%28n%2F2%29%28a%5B1%5D%2Ba%5Bn%5D%29

S%5B20%5D%22%22=%22%22expr%2820%2F2%29%282%2B59%29

S%5B20%5D%22%22=%22%22%2810%29%2861%29

S%5B20%5D%22%22=%22%22610

Edwin