Q. Find an explicit formula for the arithmetic sequence −5,13,31,49,….Note: the first term should be b(1).
b(n) = \(\square\)
Identify Type: Identify whether the given sequence is geometric or arithmetic. The sequence −5,13,31,49,… has a common difference between consecutive terms, so it is an arithmetic sequence.
Find Common Difference: Determine the common difference, d, by subtracting the first term from the second term: d=13−(−5)=18.
Use Explicit Formula: Use the explicit formula for an arithmetic sequence, b(n)=b(1)+(n−1)d, where b(1) is the first term and d is the common difference. For the sequence −5,13,31,49,…, the first term, b(1), is −5 and the common difference, d, is 18.
Substitute Values: Substitute the values of b(1) and d into the formula to write an expression to describe the sequence. The expression for the sequence is b(n)=−5+(n−1)×18.
Simplify Expression: Simplify the expression to get the final explicit formula for the sequence. b(n)=−5+18n−18, which simplifies to b(n)=18n−23.
More problems from Write a formula for an arithmetic sequence