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Mathematics

Without using trigonometric tables, evaluate the following:

cos 65°sin 25°+cos 32°sin 58°sin 28° sec 62° + cosec230°\dfrac{\text{cos 65°}}{\text{sin 25°}} + \dfrac{\text{cos 32°}}{\text{sin 58°}} - \text{sin 28° sec 62° + cosec}^2 30°

Trigonometrical Ratios

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Answer

Solving,

cos 65°sin (90° - 65°)+cos 32°sin (90° - 32°)sin 28°×1cos 62°+1sin230°cos 65°cos 65°+cos 32°cos 32°sin 28°×1cos 62°+1sin230°1+1sin 28°×1cos(90°28°)+1(12)22sin 28°sin 28°+421+45.\Rightarrow \dfrac{\text{cos 65°}}{\text{sin (90° - 65°)}} + \dfrac{\text{cos 32°}}{\text{sin (90° - 32°)}} - \text{sin 28°} \times \dfrac{1}{\text{cos 62°}} + \dfrac{1}{\text{sin}^2 30°} \\[1em] \Rightarrow \dfrac{\text{cos 65°}}{\text{cos 65°}} + \dfrac{\text{cos 32°}}{\text{cos 32°}} - \text{sin 28°} \times \dfrac{1}{\text{cos 62°}} + \dfrac{1}{\text{sin}^2 30°} \\[1em] \Rightarrow 1 + 1 - \text{sin 28°} \times \dfrac{1}{cos(90° - 28°)} + \dfrac{1}{\Big(\dfrac{1}{2}\Big)^2} \\[1em] \Rightarrow 2 - \dfrac{\text{sin 28°}}{\text{sin 28°}} + 4 \\[1em] \Rightarrow 2 - 1 + 4 \\[1em] \Rightarrow 5.

Hence, cos 65°sin 25°+cos 32°sin 58°sin 28° sec 62° + cosec230°\dfrac{\text{cos 65°}}{\text{sin 25°}} + \dfrac{\text{cos 32°}}{\text{sin 58°}} - \text{sin 28° sec 62° + cosec}^2 30° = 5.

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