So, we must find the sum of this arithmetic sequence -1,2,5,8,11,14,17
using the arithmetic sequence formula and Sum of an Arithmetic Sequence formula such that an =
a1 + d(n-1)...........where a1 = -1 and a2 = 2.
We can use this information to find the common sum ratio 'd' such that,a2 = a1 + d(2-1)2 = -1 + d(1)...........Then add 1 to both sides to get 3
= We do not need d to find the sum but i decided to show you how to find 'd' in case you needed to find the nth term.
The Sum Formula yields,Sn = n(a1 + a7) / 2,
where n is the number if terms which is 7 in this case, right ?
Then we plug in the first and seventh terms for a1 and a7 such that=
S(7)=
(7)(-1+17) / 2 = (7)(16/2) = (7)(8) = 56
I hope this helped!
Aliyyah.