Question

The sum of the first n term of an a.p. is n/2(3n+13) .Find it's 30th term

Answer 1

as we know 
Sum of first n terms of an AP is 
(n/2)(2a+nd-d)
equating it to n/2(3n+13) gives you a=5 and d=3
so the 30th term will be
=a+(n-1)d
=5+(29)3
=5+87
=92