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Question: If in the expansion of \(\left( \sqrt{3} + \sqrt[8]{5} \right)^{256}\), the coefficients of \(a_{r}\...

If in the expansion of (3+58)256\left( \sqrt{3} + \sqrt[8]{5} \right)^{256}, the coefficients of ara_{r} and xrx^{r} be equal, then r is equal to.

A

9

B

10

C

11

D

12

Answer

10

Explanation

Solution

(2n)!3!3!(2nm)!\frac{(2n)!3!3!}{(2n - m)!}

(2n)!(2nm3)!(4n+m3)!\frac{(2n)!}{\left( \frac{2n - m}{3} \right) ⥂ !\left( \frac{4n + m}{3} \right)!}Coefficient of (1+x)n(1 + x)^{n} and coefficient of

n29nn^{2} - 9n

So, we must have (1+x+x3+x4)10,(1 + x + x^{3} + x^{4})^{10},.