The Total solution for NCERT class 6-12
In the given A.R 9,12, 15, 18, …First term (a) = 9and common difference (d) = 12 – 9 = 3and an = a + (n – 1) dNow a36 = a + (36 – 1) d = 9 + 35 x 3 = 9 + 105 = 114Let the an be the required terman = a + (n – 1) d= 9 + (n – 1) x 3 = 9 + 3n – 3 = 6 + 3nBut their difference is 39an – a36 = 39=> 6 + 3n – 114 = 39=> 114 – 6 + 39 = 3n=> 3n = 147=> n = 49Required term is 49th