9. If $a_{1}=2$ and $a_{n}=a_{n-1}-4$ then find the value of $a_{4}$.

Step 1 ：The given sequence is a recursive sequence where each term is 4 less than the previous term.

Step 2 ：We can find the value of \(a_{4}\) by applying the formula \(a_{n}=a_{n-1}-4\) three times starting from \(a_{1}=2\).

Step 3 ：\(a_{4} = a_{3} - 4\)

Step 4 ：\(a_{3} = a_{2} - 4\)

Step 5 ：\(a_{2} = a_{1} - 4\)

Step 6 ：Substituting \(a_{1} = 2\) into \(a_{2} = a_{1} - 4\), we get \(a_{2} = 2 - 4 = -2\)

Step 7 ：Substituting \(a_{2} = -2\) into \(a_{3} = a_{2} - 4\), we get \(a_{3} = -2 - 4 = -6\)

Step 8 ：Substituting \(a_{3} = -6\) into \(a_{4} = a_{3} - 4\), we get \(a_{4} = -6 - 4 = -10\)

Step 9 ：Final Answer: The value of \(a_{4}\) is \(\boxed{-10}\)