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{[f(1)=72],[f(n)=f(n-1)+9]:}
Find an explicit formula for 
f(n).

f(n)=

{f(1)=72f(n)=f(n1)+9 \left\{\begin{array}{l} f(1)=72 \\ f(n)=f(n-1)+9 \end{array}\right. \newlineFind an explicit formula for f(n) f(n) .\newlinef(n)= f(n)=

Full solution

Q. {f(1)=72f(n)=f(n1)+9 \left\{\begin{array}{l} f(1)=72 \\ f(n)=f(n-1)+9 \end{array}\right. \newlineFind an explicit formula for f(n) f(n) .\newlinef(n)= f(n)=
  1. Identify Sequence Type: Identify the type of sequence described by the function f(n)f(n). The function f(n)=f(n1)+9f(n) = f(n-1) + 9 suggests that this is an arithmetic sequence because there is a constant difference between consecutive terms.
  2. Determine First Term: Determine the first term of the sequence. We are given that f(1)=72f(1) = 72, which means the first term, a1a_1, is 7272.
  3. Find Common Difference: Determine the common difference of the sequence. The function f(n)=f(n1)+9f(n) = f(n-1) + 9 indicates that the common difference, dd, is 99 because each term is 99 more than the previous term.
  4. Use Explicit Formula: Use the explicit formula for an arithmetic sequence, which is an=a1+(n1)da_n = a_1 + (n-1)d. Substitute the values of a1a_1 and dd into the formula. In this case, a1=72a_1 = 72 and d=9d = 9.
  5. Write Formula: Write the explicit formula for the sequence using the values from Step 22 and Step 33. The formula is f(n)=72+(n1)×9f(n) = 72 + (n-1)\times9.
  6. Simplify Formula: Simplify the formula. Multiply 99 by (n1)(n-1) to get 9n99n - 9. Add this to the first term, 7272, to get f(n)=72+9n9f(n) = 72 + 9n - 9.
  7. Combine Like Terms: Combine like terms to get the final explicit formula. f(n)=9n+729f(n) = 9n + 72 - 9 simplifies to f(n)=9n+63f(n) = 9n + 63.

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