What is the number of rational terms in the expansion of \((\sqrt{3}+5^\frac{1}{4})^{12}\)

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NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. 2
  2. 3
  3. 4
  4. 6

Answer (Detailed Solution Below)

Option 3 : 4
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Detailed Solution

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Concept:

A term in the binomial expansion of (a + b)n is given by Tk+1 = C(n, k) × an-k × bk.

For a term to be rational, the exponents of both √3 and 51/4 must be integers.

Formula Used:

In (√3)n-k, n-k must be even for it to be rational.

In (51/4)k, k must be a multiple of 4 for it to be rational.

Calculation:

Let n = 12:

⇒ For √3n-k to be rational, n-k must be even.

⇒ Since n = 12, k must also be even.

⇒ For (51/4)k to be rational, k must be a multiple of 4.

⇒ The values of k that satisfy both conditions (k is even and a multiple of 4) are:

⇒ k = 0, 4, 8, and 12.

⇒ These correspond to 4 rational terms in the expansion.

Hence, the Correct answer is Option 3. 

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