A is 1 and D is 3....so find number of terms by sum of the AP...that will give you a quadratic of n....in that you have to neglect negative value of n(if there are any)..coZ number of terms cannot be negative...
So now you have got number of terms...you know X is the last terms or nth term of the series....so...you can easily find X now...
Written on Dec. 4, 2017, 1:31 a.m.