Angle X is defined as the length, a, the arc that extends the angle divided by the radius, r, of
the circle: X = a/r.
2 Pi rad = 360 degrees or Pi rad = 180 degrees.
To convert degrees to radians, multiply degree measure with Pi/180.
To convert radian measure to degrees, multiply radian measure with 180/Pi.
Trigonometric ratios and special angles
You can use a calculator to calculate trigonometric ratios for an angle expressed in radian
measure by setting the angle mode to radians.
You can determine the reciprocal trigonometric ratios for an angle expressed in radian measure
by first calculating the primary trigonometric ratios then using the reciprocal key on the
You can also use the unit circle and special triangles to determine exact values for the
trigonometric ratios of the special angles 0, Pi/6, Pi/3. Pi/4, and Pi/2.
You can use the unit circle along with the CAST rule to determine exact values for the
trigonometric ratios of multiples of the special angles.
Equivalent Trigonometric Expressions
You can use a right triangle to derive equivalent trigonometric expressions that form the
cofunction identities, such as sinx = cos(Pi/2 – x).
You can use the unit circle along with transformations to derive equivalent trigonometric
expressions that form other trigonometric identities, such as cos(Pi/2 + X) = -sinx
Given a trigonometric expression of a known angle, you can use the equivalent trigonometric
expressions to evaluate trigonometric expressions of other angles.
You can use graphing technology to demonstrate that two trigonometric expressions