The first five terms of a sequence are "a" Subscript, 1 , Baseline equals 47 , "a" Subscript, 2 , Baseline equals 33 , "a" Subscript, 3 , Baseline equals 19 , "a" Subscript, 4 , Baseline equals 5 , "a" Subscript, 5 , Baseline equals negative 9.a1​=47, a2​=33, a3​=19, a4​=5, a5​=−9.

Based on this information, create an equation that can be used to find the nth term of the sequence, "a" Subscript, "n" , Baselinean​.

1 answer

To find a general formula for the \( n \)-th term of the sequence given:

  • \( a_1 = 47 \)
  • \( a_2 = 33 \)
  • \( a_3 = 19 \)
  • \( a_4 = 5 \)
  • \( a_5 = -9 \)

we first observe the differences between consecutive terms.

  1. \( a_2 - a_1 = 33 - 47 = -14 \)
  2. \( a_3 - a_2 = 19 - 33 = -14 \)
  3. \( a_4 - a_3 = 5 - 19 = -14 \)
  4. \( a_5 - a_4 = -9 - 5 = -14 \)

The sequence has a constant difference of \(-14\), indicating that it is an arithmetic sequence.

The general form for the \( n \)-th term of an arithmetic sequence can be expressed as:

\[ a_n = a_1 + (n - 1) \cdot d \]

where:

  • \( a_1 \) is the first term of the sequence,
  • \( d \) is the common difference,
  • \( n \) is the term number.

Substituting the values we have:

  • \( a_1 = 47 \)
  • \( d = -14 \)

Thus, the formula becomes:

\[ a_n = 47 + (n - 1)(-14) \]

We can simplify this expression:

\[ a_n = 47 - 14(n - 1) \] \[ a_n = 47 - 14n + 14 \] \[ a_n = 61 - 14n \]

Therefore, the equation to find the \( n \)-th term of the sequence is:

\[ a_n = 61 - 14n \]