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GATE DA 2024 Q60: Limit of ln((x²+1) cos x) / x² as x → 0

Question

Evaluate the following limit:

lim⁡x→0ln⁡((x2+1)cos⁡x)x2\lim_{x \to 0} \frac{\ln\left((x^2 + 1)\cos x\right)}{x^2}

The value of the limit is ______.

Try it: numerical answer: type the value

Numerical answer. No negative marking.
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Answer: 0.5 (official GATE 2024 final answer key)

Concept used: Limits using series expansions: ln⁡(1+u)≈u\ln(1+u) \approx u and cos⁡x≈1−x22\cos x \approx 1 - \tfrac{x^2}{2} near 0.

First step: Split the log: ln⁡(1+x2)+ln⁡cos⁡x≈x2−x22\ln(1 + x^2) + \ln \cos x \approx x^2 - \tfrac{x^2}{2}.

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Source: official GATE 2024 DA question paper and final answer key, organised by IISc Bangalore. Question paper · Answer key