Find a8 and a15 whose nth term is

Find a8 and a15 whose nth term is

Solution :

In a8, 8 is even in a15, 15 is odd 

an  = (n2 - 1)/(n + 3) a8  = (82 - 1)/(8 + 3)   =  (64 - 1)/11   =  63/11

an  = n2/(2n + 1) a15  = 152/(2(15) + 1)   =  225/(30 + 1)   =  225/31