Question

Q21) The sum of n terms of an AP is given by Sn=(2n²+3n). What is the common difference of the AP?

Answer 1

Hi there!!

See, it works like this......

I have two methods for solving this question, first for subjective and second for objective tests. They are as follows......

First :-

Placing 1 in place of n to get value of first term, we get....

2(1^2)+3(1) = 5

Therefore, a = 5

Now, the sum of a and a + d, will be got by placing the value of n as 2 .....

2(2^2)+3(2) = (a) + (a + d)

Now after placing the value of a = 5 and solving the equation we get.....

d = 4

Second :-

You have to just twice the value of the coefficient of n^2 and you will be getting the value.

Here, the coefficient of n^2 is 2 and multiplying it with 2, we get the same answer which is 4.

Hope you like my typing efforts !!