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Question
Express each one of the following in terms of trigonometric ratios of angles lying between 0° and 45°
cos 78° + sec 78°
Solution
We know `sec(90^@ - theta) = cosec theta` and `cos (90^2 - theta) = sin theta`
`cos 78^@ + sec 78^@ = cos(90^@ - 12^@) + sec (90^@ - 12^@)`
`= sin 12^@ + cosec 12^@`
Thus the desired expression is `sin 12^@ + cosec 12^@`
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