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If the number of terms free from radical...

If the number of terms free from radicals in the expansion of `(7^((1)/(3))+11^((1)/(9)))^(6561)` is k, then the value of `(k)/(100)` is equal to

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To solve the problem, we need to find the number of terms free from radicals in the expansion of \((7^{\frac{1}{3}} + 11^{\frac{1}{9}})^{6561}\). ### Step-by-Step Solution: 1. **Identify the General Term**: The general term \(T_{r+1}\) in the binomial expansion of \((a + b)^n\) is given by: \[ T_{r+1} = \binom{n}{r} a^{n-r} b^r \] Here, \(a = 7^{\frac{1}{3}}\), \(b = 11^{\frac{1}{9}}\), and \(n = 6561\). 2. **Write the General Term for Our Case**: Substituting the values, we have: \[ T_{r+1} = \binom{6561}{r} (7^{\frac{1}{3}})^{6561-r} (11^{\frac{1}{9}})^r \] Simplifying this, we get: \[ T_{r+1} = \binom{6561}{r} 7^{\frac{6561 - r}{3}} 11^{\frac{r}{9}} \] 3. **Determine Conditions for Integer Terms**: For \(T_{r+1}\) to be an integer, both exponents \(\frac{6561 - r}{3}\) and \(\frac{r}{9}\) must be non-negative integers. This leads us to the following conditions: - \(6561 - r \equiv 0 \mod 3\) - \(r \equiv 0 \mod 9\) 4. **Find Values of \(r\)**: From the first condition, \(r\) must be congruent to \(0 \mod 3\). From the second condition, \(r\) must be a multiple of \(9\). Therefore, \(r\) can take values of \(0, 9, 18, \ldots, 6561\). 5. **Count the Valid Values of \(r\)**: The values of \(r\) that satisfy both conditions can be expressed as: \[ r = 9k \quad \text{where } k = 0, 1, 2, \ldots, \frac{6561}{9} \] The maximum value of \(k\) is: \[ k = \frac{6561}{9} = 729 \] Thus, \(k\) can take values \(0, 1, 2, \ldots, 729\), which gives us a total of \(729 + 1 = 730\) values (including \(r = 0\)). 6. **Final Calculation**: The number of terms free from radicals is \(k = 730\). We need to find \(\frac{k}{100}\): \[ \frac{k}{100} = \frac{730}{100} = 7.3 \] ### Conclusion: The value of \(\frac{k}{100}\) is \(7.3\).
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