Solving More Complex Trigonometric Equations
Cosine equations require careful attention to quadrants. When solving cosθ = 0.4, remember that cosine is positive in quadrants I and IV. Using the inverse function, we find our reference angle is 66.4°, giving us solutions at 66.4° and 293.6° or360°−66.4°.
Working with reciprocal functions like secant, cosecant, and cotangent requires an extra step. For example, with secθ = 2, first convert to cosθ = 1/2, then solve normally. This gives solutions at 60° in quadrant I and 300° in quadrant IV.
When tackling equations like cotθ = -4, convert to tanθ = -1/4, find the reference angle (14.0°), and place it in quadrants where tangent is negative. Your solutions will be 166.0° and 346.0°.
Remember: Reciprocal functions have the same sign patterns as their parent functions. Secant matches cosine, cosecant matches sine, and cotangent matches tangent.