WBJEE · Maths · Binomial Theorem
If in the expansion of \((a-2 b)^{\mathrm{n}}\), the sum of the 5 th and 6 th term is zero, then the value of \(\frac{\mathrm{a}}{\mathrm{b}}\) is
- A \(\frac{\mathrm{n}-4}{5}\)
- B \(\frac{2(n-4)}{5}\)
- C \(\frac{5}{n-4}\)
- D \(\frac{5}{2(n-4)}\)
Answer & Solution
Correct Answer
(B) \(\frac{2(n-4)}{5}\)
Step-by-step Solution
Detailed explanation
\[ \text { Hints: } \begin{gathered} (a-2 b)^{\mathrm{n}}=\sum_{\mathrm{r}=0}^{\mathrm{n}}{ }^{\mathrm{n}} \mathrm{C}_{\mathrm{r}}(a)^{\mathrm{n}-\mathrm{r}}(-2 \mathrm{~b})^{\mathrm{r}} \\ \mathrm{t}_5+\mathrm{t}_6=0 \end{gathered} \]…
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