If 26 ( 233 (12C2 )+ 255 (12C4 )+ 277 (12C6 ) . .+ + 21313 (12C12 ) )=313- , then is equal to :
- 45
- 48
- 51
- 54
Answer
(3) 51
Solution
General term: 2k+1k+1 (12Ck ), k=2, 4, , 12
1k+1 12Ck= 113 13Ck+1
26 2k+1k+1 12Ck=2 13Ck+1 2k+1
Put r=k+1=3, 5, , 13: LHS =2 r=3, 5, , 1313Cr 2r
(1+2)13-(1-2)13=2 r odd13Cr 2r r odd13Cr 2r= 313+12
The term r=1 is 13C1 2=26
LHS =2 ( 313+12-26 )=313+1-52=313-51
=51
Answer: (3)