Here, a = 21, d = – = – and if a_n = – , we have to find n.

As a_n = a + ( n – 1) d,

we have – = 21 + (n – 1)(– )

– = – n

– = – n

So, n =

Therefore, the 35th term of the given AP is – 81

Next, we want to know if there is any n for which a_n = 0. If such n is there, then

a + (n - 1) d = 0

+ (n – 1) (–) = 0,

i.e., (n – 1) =

i.e., n =

So, the eighth term is .