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Mathematics

Evaluate:

cos 55°sin 35°\dfrac{\text{cos 55°}}{\text{sin 35°}} + cot 35°tan 55°\dfrac{\text{cot 35°}}{\text{tan 55°}}

Trigonometric Identities

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Answer

cos 55°sin 35°+cot 35°tan 55°=cos (90° - 45°)sin 35°+cot (90° - 55°)tan 55°=sin 45°sin 35°+tan 55°tan 55°=sin45°sin35°+tan55°tan55°=1+1=2\dfrac{\text{cos 55°}}{\text{sin 35°}} + \dfrac{\text{cot 35°}}{\text{tan 55°}}\\[1em] = \dfrac{\text{cos (90° - 45°)}}{\text{sin 35°}} + \dfrac{\text{cot (90° - 55°)}}{\text{tan 55°}}\\[1em] = \dfrac{\text{sin 45°}}{\text{sin 35°}} + \dfrac{\text{tan 55°}}{\text{tan 55°}}\\[1em] = \dfrac{\cancel{sin 45°}}{\cancel{sin 35°}} + \dfrac{\cancel{tan 55°}}{\cancel{tan 55°}}\\[1em] = 1 + 1\\[1em] = 2

Hence, cos 55°sin 35°+cot 35°tan 55°\dfrac{\text{cos 55°}}{\text{sin 35°}} + \dfrac{\text{cot 35°}}{\text{tan 55°}} = 2.

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