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Find an explicit formula for the arithmetic sequence

81,54,27,0,dots". "
Note: the first term should be 
a(1).

a(n)=

Find an explicit formula for the arithmetic sequence\newline81,54,27,0,..  81,54,27,0, \ldots \text {.. } \newlineNote: the first term should be a a (11).\newline a(n) = \(\square\)

Full solution

Q. Find an explicit formula for the arithmetic sequence\newline81,54,27,0,..  81,54,27,0, \ldots \text {.. } \newlineNote: the first term should be a a (11).\newline a(n) = \(\square\)
  1. Identify Sequence Type: Identify whether the given sequence is geometric or arithmetic. The sequence 81,54,27,0,81, 54, 27, 0, \ldots has a common difference between consecutive terms, so it is an arithmetic sequence.
  2. Find First Term and Difference: Determine the first term (a1a_1) and the common difference (dd) of the sequence. The first term a1a_1 is 8181. To find the common difference, subtract the second term from the first term: d=5481=27d = 54 - 81 = -27.
  3. Use Explicit Formula: Use the explicit formula for an arithmetic sequence, an=a1+(n1)da_n = a_1 + (n-1)d, where a1a_1 is the first term and dd is the common difference. For this sequence, a1=81a_1 = 81 and d=27d = -27.
  4. Substitute Values: Substitute the values of a1a_{1} and dd into the formula to write an expression to describe the sequence. The expression for the sequence 81,54,27,0,81, 54, 27, 0, \ldots is an=81+(n1)(27)a_{n} = 81 + (n-1)(-27).
  5. Simplify Expression: Simplify the expression to find the explicit formula. an=8127(n1)=8127n+27=10827na_{n} = 81 - 27(n-1) = 81 - 27n + 27 = 108 - 27n.

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