Question

What is the principal value of cos inverse cos680?

Answer 1

Answer:

We write this mathematically as follows :

Cos ⁻¹ { Cos 680°) }

Cos ⁻¹ {Cos (4π - 40°) }

4π = 360 × 2 = 720

720 - 40 = 680°

Cos ⁻¹ {Cos (4π - 40)}

= Cos ⁻¹ (Cos 40) = 40

= 40°.