SOLUTION: Find the sum of the first 40 terms of the arithmetic sequence: 17, 24, 31, 38...

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Question 278426: Find the sum of the first 40 terms of the arithmetic sequence: 17, 24, 31, 38...
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
a%5B1%5D=17 d=a%5B2%5D-a%5B1%5D=24-17=7, n=40
`
S%5Bn%5D=%28n%2F2%29%282a%5B1%5D%2B%28n-1%29%2Ad%29
S%5B40%5D=%2840%2F2%29%282%2A17%2B%2840-1%29%2A7%29
S%5B40%5D=20%2834%2B39%2A7%29
S%5B40%5D=20%2834%2B273%29
S%5B40%5D=20%28307%29
S%5B40%5D=6140
`
17+24+31+38+45+52+59+66+73+80+87+94+101+108+115+122+129+136+143+150
+157+164+171+178+185+192+199+206+213+220+227+234+241+248+255+262+269
+276+283+290 = 6140
`
Edwin