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Evaluate: 3 cos 80° cosec 10°+ 2 sin 59° sec 31°

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Question

Evaluate:

3 cos 80° cosec 10°+ 2 sin 59° sec 31°

Evaluate
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Solution

3 cos 80° cosec 10° + 2 sin 59° sec 31°

= 3 cos 80° cosec (90° – 80°) + 2 sin 59° sec (90° – 59°)

= 3 cos 80° sec 80° + 2 sin 59° cosec 59°

= 3 × 1 + 2 × 1  ...(∵ cos A × sec A = 1)

= 3 + 2

= 5   

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Chapter 21: Trigonometrical Identities - Exercise 21 (C) [Page 328]

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Selina Concise Mathematics [English] Class 10 ICSE
Chapter 21 Trigonometrical Identities
Exercise 21 (C) | Q 5. (ii) | Page 328
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