Question

Find an A.P. in which the sum of any number of terms is always three times the squared number of these terms.

Answer 1

AP-.a,d
`n/2[2a+(n-1)d]=3n^2`
`2a+(n-1)d=6n`
`2a+(d-6)n-d=0`
`d-6=0`
`d=6`
`2a-d=0`
`2a=6`
`a=3`.