Question

Express the following in terms of trigonometric ratios of angles lying between 0° and 45°.

cos 78° + sec 78°

Answer 1

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^@`