\(\sin \frac{{21\pi }}{2}\) और cos(-1740°) का मान ज्ञात कीजिये?

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AAI ATC Junior Executive 25 March 2021 Official Paper (Shift 1)
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  1. \(\frac{{\sqrt 3 }}{2},\frac{1}{2}\)
  2. \(\frac{{\sqrt 3 }}{2},\frac{1}{{\sqrt 2 }}\)
  3. \(0,\frac{1}{{\sqrt 2 }}\)
  4. \(1,\frac{1}{2}\)

Answer (Detailed Solution Below)

Option 4 : \(1,\frac{1}{2}\)
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संकल्पना:​​​​​

cos (-θ) = cos θ

cos (2nπ - θ) = cos θ

डिग्री में कोण  0°  30° 45° 60° 90°
sin  0 1/2 \(1/\sqrt2\) \(\sqrt3/2\) 1
cos 1 \(\sqrt3/2\) \(1/\sqrt2\) 1/2 0
tan 0 \(1/\sqrt3\) 1 \(\sqrt3\) अपरिभाषित 

गणना:

हमारे पास है, 

⇒ \(sin(\frac{21π}{2})\)

जब तक कोण 0 और 2π के बीच न हो जाए, तब तक 2π का पूरा घुमाव हटा दें।

⇒ \(sin(\frac{21π}{2})= sin(5\times 2\pi +\frac{π}{2}) =sin(\frac{π}{2})\)

जैसा कि हम जानते हैं कि \(sin(\frac{π}{2})\) का मान 1 है

जैसा कि हम जानते हैं, cos θ का मान 2π या 360° के अंतराल के बाद दोहराता है।

⇒ cos (-1740°) = cos (1740°)    [∵ cos (-θ) = cos θ]

हम जानते हैं कि cos (2nπ - θ) = cos θ

चूँकि sin θ और cos θ का आवर्तकाल 360° है।

⇒ cos (1740°) = cos (5 × 360° - 1740°)

⇒ cos (1740°) = cos (1800° - 1740°)

⇒ cos (1740°) = cos (60°)

 हम जानते हैं कि, cos 60° = 1/2

⇒ cos (-1740°) = 1/2.

\(\sin \frac{{21\pi }}{2}\) का मान 1 है और cos (-1740°) का मान 1/2 है

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