Please explain both parts still didn't get it ...
It's given that the nth term is n(n+1)/k where k comes out to be 2.
so, (n+1)th term will be (n+1)(n+2)/k where k is 2. (v'll add 1 because it's n+1 and not n)
so v'll do this now:
(n(n+1))/2 + ((n+1)(n+2))/2
=(n^2+n+n^2+2n+n+2)/2
=(2n^2+4n+2)/2
=(2(n^2+2n+1))/2
=n^2+2n+1
So, n^2+2n+1=(n+1)^2
Now v have to find 2 consecutive terms with sum of 3481.
v got frm d above ans that the sum of two consecutive nos. is (n+1)^2
now v'll use that and make it equal to 3481 as given below
(n+1)^2=3481
n^2+2n+1=3481
n^2+2n-3480=0
n=(-2+-underroot(2^2-4*1*-3480))/2
n=(-2+-underroot(13924))/2
n=(-2+-118)/2
So, n=58, -60
n=58 (It can't be negative)
Two terms will be n, (n+1)
=58, 59
(58(58+1))/2=1711
(59(59+1))/2=1770
Answer=1711 and 1770
hope u get it now!!
