Question

In the expansion of $\left( \sqrt[3]{\frac{a}{b}} + \sqrt[3]{\frac{b}{\sqrt{a}}} \right)^{21}$ the term containing same powers of a and b is –

• A. 11^th
• B. 13^th
• C. 12^th
• D. 6^th

Answer 1

Answer: (B)

13^th

Answer 2

General term = T_r+1

= ²¹C_r$\frac{b^{r/3}}{a^{r/6}}$ = ²¹C_r $a ^ { \frac { 41 - 3 r } { 6 } }$ $b^{\frac{2r - 21}{3}}$

̃ r = 12 ̃ 13^th term