**The steps to prove whether a given number sequence is an arithmetic progression.**Step 1: List down any three consecutive terms. [Example: T 1 , T 2 , T 3 .]

Step 2: Calculate the values of T 3 − T 2 and T 2 − T 1 .

Step 3: If T 3 − T 2 = T 2 − T 1 =d, then the number sequence is an arithmetic progression.

[Try Question 8 and 9 in SPM Practice 1 (Arithmetic Progression)]

**Example :**

Prove whether the following number sequence is an arithmetic progression

(a) 7, 10, 13,….

(b) -20, -15, -9 ,……