If r=19 ( r+32r ) 9Cr = ( 32 )9 - , , N, then ( + )2 is equal to
- 27
- 81
- 18
- 9
Answer
(2) 81
Solution
S = r=19 r 9Cr ( 12 )r + 3 r=19 9Cr ( 12 )r
r 9Cr = 9 8Cr-1
r=19 r 9Cr ( 12 )r = 92 r=19 8Cr-1 ( 12 )r-1 = 92 ( 32 )8 = 3 ( 32 )9
r=19 9Cr ( 12 )r = ( 32 )9 - 1
S = 3 ( 32 )9 + 3 ( 32 )9 - 3 = 6 ( 32 )9 - 3
= 6, = 3
( + )2 = 92 = 81
Answer: (2)