Sum of first p terms = Sp = (ap2 + bp)
Sum of one term = S1 = a(1)2 + b(1) = a+b = first term
Sum of first two terms = S2 = a(2)2 + b x 2 = 4a + 2b
We know that, second term = a2 = S2 – S1
= (4a + 2b) – (a + b)
= 3a + b
Now, d = a2 – a1
= 3a + b – (a+b)
= 2a
Answer: Common difference is 2a.