Find an explicit formula for the arithmetic sequence

\[-2,-14,-26,-38,\unicode{0x2026}\].
Note: the first term should be
\[\text{\it{d(1)}}\].
\[d(n)=\]

1 answer

An arithmetic sequence can be expressed in the form:

\[ d(n) = a + (n - 1) \cdot r \]

where \( a \) is the first term, \( n \) is the term number, and \( r \) is the common difference between the terms.

In the given sequence:

  • The first term \( a = -2 \).
  • To find the common difference \( r \), we can calculate the difference between any two consecutive terms. For example:

\[ r = -14 - (-2) = -14 + 2 = -12 \]

We can verify this by checking the next pair:

\[ -26 - (-14) = -26 + 14 = -12 \]

\[ -38 - (-26) = -38 + 26 = -12 \]

The common difference \( r = -12 \) is consistent between the terms.

Now, substituting \( a \) and \( r \) into the formula for an arithmetic sequence, we get:

\[ d(n) = -2 + (n - 1) \cdot (-12) \]

This simplifies to:

\[ d(n) = -2 - 12(n - 1) \]

Expanding the expression gives:

\[ d(n) = -2 - 12n + 12 \] \[ d(n) = 10 - 12n \]

Thus, the explicit formula for the arithmetic sequence is:

\[ \boxed{d(n) = 10 - 12n} \]