If n is an odd natural number , then n∑r=0(−1)rrCr equals :
1/n
n/2n
0
None
Let n = 2k+1 then n∑r=0(−1)rnCr=2k+1∑r=0(−1)2k+12k+1Cr
= n∑r=0(−1)rnCr=2k+1∑r=0(−1)2k+12k+1Cr=12k+1Cr−12k+1C1+....+12k+1C2k−12k+1C2k+1=0
If n is an even natural number , then n∑r=0(−1)rnCrequals: