Question

Hey :)
I was wondering if someone could tell me if this answer and working is correct or not...

Cos theta =-0.25
Cos inverse -0.25 = -14
therefore theta equals:
180--14=194or/and
180+-14=166

Any help would be much appreciated :)
Thanks!

Answer 1

cos (theta) = -0.25
theta = cos^-1 (-0.25)

there are two answers:
theta = 104.48 degrees = 3.65 radians
and,
theta = -104.48 degrees = -3.65 radians

hope this helps~ :)

Answer 2

Usually the required angles are in the domain of
0 ≤ Ø ≤ 360°

Since the given cosØ is negative, by the CAST rule,
Ø must be in either quadrant II or III
from cosØ = +.25 we get the reference angle of 75.52°
so Ø = 180°-75.52° or 104.48° (Jai's answer)
or Ø = 180°+75.52° or 255.52°

Since the period of cosØ is 360°, you can get other answers by adding or subtracting multiples of 360°
(For Jai's second answer, 255.52 - 360° = 104.48°)

I have no idea how you came up with
inverse cos (-.25) = -14