The value of n∑r=0(−1)rnCrr+2 is equal to .
C0x−C1x2+C2x3.......=x(1−x)n
Integrating both sides , within the limits 0 to 1
[(C0x22−C1x33+C2x44−.......)]10=∫10x(1−x)ndx
∫10(1−x)xndx=[xn−1n+1−xn+2n+2]10
⇒ C02−C13+C24−....=1(n+1)−1(n+2)=1(n+1)(n+2).