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JEE Mains · Maths · STD 11 - 12. limits

If \(\alpha=\lim _{x \rightarrow \pi / 4} \frac{\tan ^{3} x-\tan x}{\cos \left(x+\frac{\pi}{4}\right)}\) and \(\beta=\lim _{x \rightarrow 0}(\cos x)^{\operatorname{cotx}}\) are the roots of the equation, \(a x^{2}+b x-4=0\), then the ordered pair \((\mathrm{a}, \mathrm{b})\) is :

  1. A \((1,-3)\)
  2. B \((-1,3)\)
  3. C \((-1,-3)\)
  4. D \((1,3)\)
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Answer & Solution

Correct Answer

(D) \((1,3)\)

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Detailed explanation

\(\alpha=\lim _{x \rightarrow \frac{\pi}{4}} \frac{\tan ^{3} x-\tan x}{\cos \left(x+\frac{\pi}{4}\right)} ; \frac{0}{0}\) form Using L Hopital rule \(\alpha=\lim _{x \rightarrow \frac{\pi}{4}} \frac{3 \tan ^{2} x \sec ^{2} x-\sec ^{2} x}{-\sin \left(x+\frac{\pi}{4}\right)}\)…
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