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Find the sum of the arithmetic sequence -1,2,5,8,11,14,17

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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.

User Vadonka
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