JEE Mains · Maths · STD 11 - 7. binomial theoram
Suppose A and B are the coefficients of \(30^{\text {th }}\) and \(12^{\text {th }}\) terms respectively in the binomial expansion of \((1+x)^{2 \mathrm{n}-1}\). If \(2 \mathrm{~A}=5 \mathrm{~B}\), then n is equal to :
- A 22
- B 20
- C 21
- D 19
Answer & Solution
Correct Answer
(C) 21
Step-by-step Solution
Detailed explanation
\begin{aligned} & \mathrm{A}={ }^{2 \mathrm{n}-1} \mathrm{C}_{29} \quad \mathrm{~B}={ }^{2 \mathrm{n}-1} \mathrm{C}_{11} \\ & 2^{2 \mathrm{n}-1} \mathrm{C}_{29}=5{ }^{2 \mathrm{n}-1} \mathrm{C}_{11} \\ & 2 \frac{(2 \mathrm{n}-1)!}{29!(2 \mathrm{n}-30)!}=5 \frac{(2…
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