Question

Use \large S_n=\frac{n}{2}\left(a_1+a_n\right) or \large S_n=\frac{n}{2}\left(2a_1+d\left(n-1\right)\right) to find the sum of the arithmetic series when,

\large a_1=35, \large a_n=105, and \large n=8

Sum =

Answer 1

560

Explanation:

Given Sum = n/2{a1+an}

Govn the following

a1= 35

an = 105

n =8

Substitute into the expression

Sn = n/2(35+105)

Sn = n/2(140)

Sn = 70n

Sn = 70(8)

Sn = 560

Hence the sum of the AP is 560