Step 1: Identify the first term in the sequence, call this number a.

Step 2: Calculate the common difference(d) of the sequence.

Step 3: Identify the number of terms (n).

[EXAMPLE: In A.P 2, 4, 6,..... find the sum of the first 10 terms. So take n=10

Step 4: Plug the values of n, d, and a into the formula.

[FORMULA: The formula for finding the sum of first n terms of an arithmetic sequence (S_n) =(n/2)[2a + (n- 1)d]

Step 5: Simplify further..

Step 6: Make sure that the result obtained, is satisfying the given answer in the question or not.