If the nth term of the A.P.is same as the nth term of the A.P.find n.
A=9, D=7-9=-2
a=15, d=-3
An=an
A+(n -1)D=a +(n -1)d
9 – (n -1)2=15 – (n -1)3
(n -1)(3 -2)=6
n -1=6
n=7