Question
Question: Number of rational terms in the expansion (7<sup>1/3</sup> + 11<sup>1/9</sup>) <sup>6561</sup>...
Number of rational terms in the expansion (71/3 + 111/9) 6561
A
729
B
730
C
731
D
None of these
Answer
730
Explanation
Solution
Tr+1 = 6561Cr (71/3)6561 – r (111/9)r
= 6561Cr 72187. 7–r/3. 11r/9
0 £ r £ 6561
For rational terms r is multiple of 9 0, 9, 81, 27,……6561
Tn = 6561 = a +(n – 1) d = 0 + (n – 1) 9
n = 1 + 96561 = 1 + 729 = 730.