I need to find sec θ = \({2}\) in the domain \({-180° ≤ θ < 90°}\)

because sec θ = \({1 \over cosθ}\), and cos 60° = 2 (using the half equilateral triangle), i know my angles are 60°, -60°, -120°, and -180°.

but in the textbook, the answers are 60°and -60°. i'm confused? my answers fit in the domain so why aren't they considered as an answer?

Guest Jan 8, 2019

#1**+2 **

Sec = 1/cos

1/cos =2

1 = 2 cos

1/2 = cos 60 degrees and -60 degrees Cos of -120 = -1/2 cos of -180 = -1

ElectricPavlov Jan 8, 2019