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← JEE Main 2022 · 29 Jul · Shift 1
MathematicsInteger+4 / -1Question 25 of 90

JEE Main 2022 · 29 Jul · Shift 1, Mathematics question 25

Let the ratio of the fifth term from the beginning to the fifth term from the end in the binomial expansion of (24+134)n\left(\sqrt[4]2+\dfrac1{\sqrt[4]3}\right)^n, in the increasing powers of 134\dfrac1{\sqrt[4]3} be 64:1\sqrt[4]6:1. If the sixth term from the beginning is α34\dfrac\alpha{\sqrt[4]3}, then α is equal to _______.

Answer and worked solution

Official answer: 84

Ratio. T5Tn−3=2(n−4)/43−12⋅3−(n−4)/4=6(n−8)/4=61/4\dfrac{T_5}{T_{n-3}}=\dfrac{2^{(n-4)/4}3^{-1}}{2\cdot3^{-(n-4)/4}}=6^{(n-8)/4}=6^{1/4}, so n=9n=9.

Sixth term (95) 24/4 3−5/4=252334=8434\binom95\,2^{4/4}\,3^{-5/4}=\dfrac{252}{3\sqrt[4]3}=\dfrac{84}{\sqrt[4]3}.

Answer: 84