Solving Trigonometric Equations on a Specified Interval

We started to study "Solving Trigonometric Equations on a Spcifid Interval" and it shows how to get θ in degrees or radians by using CAST rule.

FORMULA EVERY QUADRANT:
QI : Ref = Rel
QII : 180 - Ref = Rel
QIII: 180 + Ref = Rel
QIV: 360 - Ref = Rel

Example: 2cosθ + = 0 over the interval

• 2cosθ + = 0
  
• 2cosθ = - : Transpose and it should be -
• : After transpose, divide both sides by 2 and,
  

• : you will know now your cosθ

Then diagram it and the reference angle should be in QII and QIII because cosθ is (-) in QII and QII

QII: 180 - =
QIII: 180 + =

θ = {, }