Hello, Tom!
You picked some incorrect angles . . .
cos(2x) = -(√3)/2, . -180° < x < 180°
Cosine is negative in Quadrants 2 and 3.
. . 2x .= .-210°, -150°, 150°, 210°
Therefore: .x .= .-105°, -75°, 75°, 105°
Can someone please check that I've got the correct answers as they don't appear to fit.
Q: cos2x = -(√3)/2 -180<=x<=180
I've got 2x=210, 330, 570, 690
x=105, 165, 285, 345
We're currently learning about using CAST diagrams to solve trigonometric equations, so if any anyone can explain in terms of CAST diagrams I'd be grateful.