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The number of terms which are free from radical signs in the expansion of \left(y^{1 / 5}+x^{1 / 10}\right)^{55} is

Option: 1

5


Option: 2

6


Option: 3

7


Option: 4

None of these


Answers (1)

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The general term in the expansion of \left(y^{1 / 5}+x^{1 / 10}\right)^{55} is

T_{r+1}={ }^{55} C_r\left(y^{1 / 5}\right)^{55-r}\left(x^{1 / 10}\right)^r={ }^{55} C_r y^{11-r / 5} x^{r / 10}

Clearly, T_{r+1} will be independent of radical signs if r/5 and r/10 are integers, where 0 \leq r \leq 55.

\therefore \quad r=0,10,20,30,40,50

Hence, there are 6 terms in the expansion of the given expression which are independent of radicals. 

Posted by

Divya Prakash Singh

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