Problem 139 of 7
Find a_4 using the sequence rule a_1 = 81; a_n = (1/3)a_(n-1).
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compute terms efficiently and interpret index.
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Rule must be explicit or recursive and target term must be computable exactly.
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Solution
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1. Identify the target term number.
2. Use the explicit formula directly or iterate the recursive rule carefully.
3. Check indexing convention.
Use the worked steps, then substitute the final answer back into the original relationship to confirm it satisfies the prompt.
Index-shift errors such as using n instead of n-1.