How do you find the sum of the first 10 terms of the arithmetic sequence, if the first term is 5 and the common difference is -8?

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Answer 1 · 2016-11-09T09:24:59

$S_10 =-310$

There is a formula for the sum of $n$ terms of an A.P.

$S_n = n/2[2a + d(n-1)]$

FRom the information given, we know that:

$n = 10 " " a= 5, " "d = -8" "$ substitute the values

$S_10 =10/2[2(5)-8((10)-1)]$

$S_10 = 5[10-80+8]$

$S-10 = 5 xx-62 = -310$