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Find an explicit formula for the arithmetic sequence 
-5,13,31,49,dots.. Note: the first term should be 
b(1).

b(n)=

Find an explicit formula for the arithmetic sequence 5,13,31,49, -5,13,31,49, \ldots .. Note: the first term should be b(1) b(1) .\newlineb(n)= b(n)=

Full solution

Q. Find an explicit formula for the arithmetic sequence 5,13,31,49, -5,13,31,49, \ldots .. Note: the first term should be b(1) b(1) .\newlineb(n)= b(n)=
  1. Identify sequence type: Identify whether the given sequence is geometric or arithmetic. The sequence 5,13,31,49,-5, 13, 31, 49, \ldots has a common difference between consecutive terms, so it is an arithmetic sequence.
  2. Determine common difference: Determine the common difference dd of the sequence by subtracting the first term from the second term. The common difference is 13(5)=1813 - (-5) = 18.
  3. Use explicit formula: Use the explicit formula for an arithmetic sequence, b(n)=b(1)+(n1)db(n) = b(1) + (n-1)d, where b(1)b(1) is the first term and dd is the common difference. For the sequence 5,13,31,49,-5, 13, 31, 49, \ldots, the first term, b(1)b(1), is 5-5 and the common difference, dd, is 1818.
  4. Write expression for sequence: Substitute the values of b(1)b(1) and dd into the formula to write an expression to describe the sequence. The expression for the sequence 5,13,31,49,extellipsis-5, 13, 31, 49, extellipsis is b(n)=5+(n1)imes18b(n) = -5 + (n-1) imes 18.
  5. Simplify expression: Simplify the expression. b(n)=5+18n18b(n) = -5 + 18n - 18, which simplifies to b(n)=18n23b(n) = 18n - 23.

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