Question

Find Sn or the sum for the given arithmetic series a1=8,d=-9,n=17

Answer 1

Here's the solution,

we know,

`\large \boxed{Sn = (n)/(2)[ 2a _1 + (n - 1)d ] }`

=》

`Sn = (17)/(2) [ (2 * 8 )+ (17 - 1) * ( - 9) ]`

=》

`Sn = (17)/(2) [16 + (16 * - 9)]`

=》

`Sn = (17)/(2) [16 + ( - 144)]`

=》

`Sn = (17)/(2) * (- 128)`

=》

`Sn = 17 * ( - 64)`

=》

`\huge\boxed{Sn = - 1088}`