Step 1: Understanding the Concept:
The common difference (\(d\)) of an Arithmetic Progression (A.P.) is the constant difference between any two consecutive terms.
Step 2: Key Formula or Approach:
\(d = a_2 - a_1\) or \(d = a_3 - a_2\), etc.
Step 3: Detailed Explanation:
The given A.P. is 1, 5, 9, ...
The first term (\(a_1\)) is 1.
The second term (\(a_2\)) is 5.
The third term (\(a_3\)) is 9.
Calculate the difference:
\[ d = a_2 - a_1 = 5 - 1 = 4 \]
To be sure, let's check the next pair:
\[ d = a_3 - a_2 = 9 - 5 = 4 \]
The difference is constant.
Step 4: Final Answer:
The common difference is 4.