If the constant term in the expansion of $\left(\frac{\sqrt[5]{3}}{x}+\frac{2 x}{\sqrt[3]{5}}\right)^{12}, x \neq 0$, is $\alpha \times 2^8 \times \sqrt[5]{3}$, then $25 \alpha$ is equal to :
Solution
<p>$$\begin{aligned}
& \left(\frac{\sqrt[5]{3}}{x}+\frac{2 x}{\sqrt[5]{3}}\right)^{12} \\
& T_{r+1}={ }^{12} C r\left(\frac{\sqrt[5]{3}}{x}\right)^{12-r}\left(\frac{2 x}{\sqrt[3]{5}}\right)^r
\end{aligned}$$</p>
<p>For constant term $-12+r+r=0$</p>
<p>$$\begin{aligned}
& \Rightarrow \quad r=6 \\
& \therefore \quad \text { Constant term }={ }^{12} C_6 \frac{(3)^{\frac{6}{5}}}{(5)^{\frac{6}{3}}}(2)^6
\end{aligned}$$</p>
<p>$$\begin{aligned}
& ={ }^{12} C_6 \times \frac{2^6}{25} \times 3.3^{\frac{1}{5}} \\
& =\frac{231}{25} \times 2^8 \cdot 3^{\frac{1}{5}} \cdot 3 \\
& =\frac{693}{25} \cdot 2^8 \sqrt[5]{3} \\
& \therefore \quad \alpha=\frac{693}{25} \\
& 25 \alpha=693
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Binomial Theorem · Topic: Binomial Expansion
This question is part of PrepWiser's free JEE Main question bank. 193 more solved questions on Binomial Theorem are available — start with the harder ones if your accuracy is >70%.