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NDA 2024 Maths · Mathematics · Limits · hard

As x approaches (π)/(2), the quotient (1-sin x)/((fracπ2-x)^2 approaches the value

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As xx approaches π2\frac{\pi}{2}, the quotient 1−sin⁡x(π2−x)2\dfrac{1-\sin x}{\left(\frac{\pi}{2}-x\right)^2} approaches the value
  1. A. 11
  2. B. 00
  3. C. 12\frac12
  4. D. 22
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Answer: (C) 12\frac12

Put h=π2−x→0h=\frac\pi2-x\to0, so sin⁡x=cos⁡h\sin x=\cos h and the expression becomes 1−cos⁡hh2→12\frac{1-\cos h}{h^2}\to\frac12. Trap: differentiating once (L'Hopital) gives −cos⁡x−2(π2−x)→00\frac{-\cos x}{-2(\frac\pi2-x)}\to\frac00 again, and stopping there or assuming the limit is 0 or 1 is common; the standard result 1−cos⁡hh2→12\frac{1-\cos h}{h^2}\to\frac12 settles it.
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