If 1 + 3 - 22 3 + 5 - 2 618 + 9 3 - 11 236 3 + 49 - 20 6180 + upto = 2 + ( ba + 1 ) e ( ab ), where a and b are integers with (a, b) = 1, then 11a + 18b is equal to .
Answer
76
Solution
Let t = 3 - 2 3 = 1 - 23: t2 = 5 - 2 63, t3 = 9 3 - 11 23 3, t4 = 49 - 20 69
S = 1 + t1 2 + t22 3 + t33 4 + t44 5 +
1n(n + 1) = 1n - 1n + 1, tnn = - e(1 - t), tnn + 1 = 1t [- e(1 - t) - t ]
S = 2 + ( 1t - 1 ) e(1 - t)
1 - t = 23, 1t - 1 = 2 3 - 2 = 6 + 2
S = 2 + 6 + 22 e 23 = 2 + ( 32 + 1 ) e ( 23 )
a = 2, b = 3 11a + 18b = 22 + 54 = 76
Answer: 76