Question

1. -18, -20, -22, -24,

find ( a_9 )

Explanation:

Step1: Identify sequence type

This is an arithmetic sequence. The first term \(a_1 = -18\), common difference \(d = -20 - (-18) = -2\).

Step2: Use arithmetic sequence formula

The formula for the \(n\)-th term of an arithmetic sequence is \(a_n = a_1 + (n - 1)d\). For \(n = 9\), substitute values: \(a_9 = -18 + (9 - 1)(-2)\).

Step3: Calculate the result

First, \(9 - 1 = 8\). Then, \(8\times(-2) = -16\). Finally, \(-18 + (-16) = -34\).

Answer:

\(-34\)