Ten > Sequence and Series
Find the sum of the series $\rm 12+9+6+\dots$ to $32$ terms
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Solution
Given:
- First term \( \rm a_1 = 12 \)
- Common difference \( \rm d = -3 \)
We can use the formula for the sum of the first \( \rm n \) terms of an arithmetic series:
\[ \rm S_n = \frac{n}{2}(2a_1 + (n - 1)d) \]
Substitute the given values:
\[ \rm S_{32} = \frac{32}{2}(2 \times 12 + (32 - 1) \times (-3)) \]
\[ \rm S_{32} = 16(24 + 31 \times (-3)) \]
\[ \rm S_{32} = 16(24 - 93) \]
\[ \rm S_{32} = 16 \times (-69) \]
\[ \rm S_{32} = -1104 \]
So, the sum of the series \(12 + 9 + 6 + \ldots\) up to 32 terms is \(-1104\).
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