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Questions  

If  n1Cr=k23nCr+1, then k is belongs to

a
(−∞,−2]
b
[2,∞)
c
[−3,3]
d
(3,2]

detailed solution

Correct option is D

∵k2−3= n−1Cr nCr+1= n−1Crnr+1n−1Cr=r+1n -----(i)∵ 0≤r≤n−1⇒ 1≤r+1≤n⇒1n≤r+1n≤1⇒ 1n≤k2−3≤1⇒ 3+1n≤k2≤4When n→∞,3

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