Binomial Theorem - Questions

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Question 1
17544

Find the fourth term in the expansion of \({(\dfrac{x}{2} - \dfrac{y}{3})^6}\)

\( - \dfrac{{5{x^3}{y^3}}}{{54}}\)

\begin{aligned}
T_{k+1}&=\left(\begin{array}{c}
n \\
k
\end{array}\right) a^{n-k} b^{k} \\
T_{4}&=\left(\begin{array}{l}
6 \\
3
\end{array}\right)\left(\frac{x}{2}\right)^{3}\left(-\frac{y}{3}\right)^{3} \\
&=20 \times \frac{x^{3}}{8} \times \frac{-y^{3}}{27} \\
\therefore T_{4}&=\frac{-5 x^{3} y^{3}}{54}
\end{aligned}

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