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Question
Evaluate the following: cos39° cos48° cos60° cosec42° cosec51°
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Solution
cos39° cos48° cos60° cosec42° cosec51°
= `cos(90° - 51°) xx cos(90° - 42°) xx (1)/(2) xx (1)/(sin42°) xx (1)/(sin51°)`
= `sin51° xx sin42° xx (1)/(2) xx (1)/(sin42°) xx (1)/(sin51°)`
= `(1)/(2)`.
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