Question

The sum of the first n terms of an A.P. is 5n2-3n. Find the A.P. and hence find its 12th
term.

Answer 1

Let n be 1
Then 5x1x2 - 3x1 =7
When n =2
The 5x1x2-3x2= 14
Similarly when n =3
It is21
So it is an ap
With a=7 abd d=7

And a+21d = 7+11x 7=154