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The sum of the first n terms of an arithmetic series is 2n(n+3).
Find the first term of the series using the formula n/2(2a+(n-1)d)

Sagot :

Answer:

Sum:

[tex]{ \bf{S _{n} = \frac{n}{2} (2a + (n - 1)d) }} \\ \\ { \sf{2n(n + 3) = \frac{n}{2}(2a + (n - 1)d) }} \\ \\ { \sf{4 {n} + 12=2a + (n - 1)d }} \\ { \sf{2a = 4n - nd + d + 12}} \\ { \sf{2a = n(4 - d) + 12 + d}} \\ { \sf{a = \frac{1}{2}(n(4 - d) + 12 + d) }}[/tex]

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