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Question
Evaluate: `(3 cos 55^@)/(7 sin 35^@) - (4(cos 70 cosec 20^@))/(7(tan 5^@ tan 25^@ tan 45^@ tan 65^@ tan 85^@))`
Solution
Cos 55° = cos (90° - 35°) = sin 35°
Cos 70° = cos (90 – 20) = sin 20°
tan 5 = cot 85° tan 25° = cot 65°
`=> (3 sin 35^@)/(7 sin 35^@) - (4(sin 20^@ cosec 20^@))/(7(cot 85^@ + tan 85^@ cot 65^@ tan 65^@ tan 45^@))`
`= 3/7 - 4/7 = -1/7`
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