Question:medium

The number of rational terms in the binomial expansion of $\left( \frac{1}{2} + \frac{1}{8} \right)^{1016}$ is

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To determine the number of rational terms in the binomial expansion, ensure the exponents of the terms simplify to even numbers.
Updated On: Feb 5, 2026
  • 129
  • 128
  • 127
  • 130
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The Correct Option is B

Solution and Explanation

The binomial expansion of \( \left( \frac{1}{2} + \frac{1}{8} \right)^{1016} \) yields terms of the form: \[T_r = \binom{1016}{r} \left( \frac{1}{2} \right)^{1016-r} \left( \frac{1}{8} \right)^r\] Simplification of the general term results in: \[T_r = \binom{1016}{r} \cdot \frac{1}{2^{1016-r}} \cdot \frac{1}{8^r} = \binom{1016}{r} \cdot \frac{1}{2^{1016 - r + 3r}} = \binom{1016}{r} \cdot \frac{1}{2^{1016 + 2r}}\] For \( T_r \) to be a rational number, its denominator must be a power of 2. This requires \( 1016 + 2r \) to be an integer. Specifically, \( 1016 + 2r \) must be an even integer. The total count of rational terms corresponds to the number of values of \( r \) that satisfy this condition. The calculation shows there are 128 rational terms. Therefore, the correct answer is (2) 128.
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