A trigonometric equation is an equation that includes the trigonometric ratio of a variable. Note these examples:
In Try This 1 you began to look at the solutions to a trigonometric equation. You may have found that a trigonometric equation will often have more than one solution between 0 and 2π and may have unlimited solutions in the real numbers.
The next activity leads you through solving a trigonometric equation that has a reciprocal trigonometric ratio and a domain in radians.
To calculate a reference angle with your calculator for a trigonometric equation, you can enter the ratio and use the sin−1 , cos−1, or tan−1 button.
Example
tan θ = 0.50, so tan−1 0.50 = 25.560 511 8…°
θ ≈ 25.6° (Calculator is in degree mode.)
tan θ = 0.50, so tan−1 0.50 = 0.463 647 609… rad.
θ ≈ 0.46 (Calculator is in radian mode.)
Complete Solving Trigonometric Equations 1. Pay attention to how a reference angle is used to solve the equation.
The notation sin−1x refers to the inverse of the sine function. The notation is not a reciprocal; but
To see another example of determining an angle given a ratio, read “Example 4” on pages 198 and 199 of the textbook.
Complete questions 10.a., 10.c., and 11.d. on page 202 of the textbook. Answer