Question

if 10th yerm of an A.P is 21 and sum of first ten terms is 120 find its n^th term

Answer 1

S= n/2(a+l)
120=10/2(a+21)
a=3
t=a+(n-1)d
21=3+(10-1)d
d=2
nth term= 3+(n-1)2
=3+2n-2
=2n+1