Question:
The total number is irrational terms in the binomial expansion of $\left(7^{1 / 5}-3^{1 / 10}\right)^{60}$ is:
Correct Option: , 4
Solution:
Let the general term of the expansion
$T_{r+1}={ }^{60} C_{r}\left(7^{\frac{1}{5}}\right)^{60-r}\left(-3^{\frac{1}{10}}\right)^{r}$
$={ }^{60} C_{r} \cdot(7)^{12-\frac{r}{5}}(-1)^{r} \cdot(3)^{\frac{r}{10}}$
Then, for getting rational terms, $r$ should be multiple of L.C.M. of $(5,10)$
Then, $r$ can be $0,10,20,30,40,50,60$.
Since, total number of terms $=61$
Hence, total irrational terms $=61-7=54$