SOLUTION: Find the sum of the first 196 terms of 2,7,12,17,.. I cant seem to figure this problem out

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Question 690880: Find the sum of the first 196 terms of 2,7,12,17,.. I cant seem to figure this problem out
Found 2 solutions by josmiceli, MathTherapy:
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
If I say +n+ is the number of
the term of the sequence starting with zero, the
sequence looks like:
+2+%2B+5%2A0+=+2+
+2+%2B+5%2A1+=+7+
+2+%2B+5%2A2+=+12+
+2+%2B+5%2A3+=+17+
----------------
To get 196 terms, I want to let +n+
run from +0+ to +195+
Summing up the terms as I started doing, I have:
+2%2A196+ + 5*( 0 + 1 + 2 + 3 + 4 + 5 + . . . + 195 )
-------------
The only difficult thing here is the summation in the parentheses
I recall that +1+%2B+2+%2B+3+%2B+4+%2B+5+%2B+6+%2B+7+%2B+8+%2B+9+%2B+10+=+%281%2F2%29%2A10%2A11+
( check it out )
So your summation is +%281%2F2%29%2A195%2A196+
+%281%2F2%29%2A195%2A196+=+%281%2F2%29%2A38220
+%281%2F2%29%2A38220+=+19110+
Now I have
+2%2A196+%2B+5%2A19110+
+392+%2B+95550+=+95942+ answer
------------------------------
I don't know any way to check the answer,
other than with some fancy calculator
or computer program.



Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
Find the sum of the first 196 terms of 2,7,12,17,.. I cant seem to figure this problem out


This is an arithmetic sequence, or A.P., and the formula for sum of an A.P.: S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29, with S%5Bn%5D+=+S%5B196%5D, 1st term, or a1%5D = 2; n, or amount of terms to be summed = 196, and d, or common difference = 5

Therefore, S%5Bn%5D+=+%28n%2F2%29%282a%5B1%5D+%2B+%28n+-+1%29d%29 becomes: S%5B196%5D+=+%28196%2F2%29%282%282%29+%2B+%28196+-+1%295%29

S%5B196%5D+=+98%284+%2B+%28195%295%29

S%5B196%5D+=+98%284+%2B+975%29

S%5B196%5D+=+98%28979%29

S%5B196%5D, or sum of the 1st 196 terms in the series = highlight_green%2895942%29

You can do the check!!

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