INVERSE TRIG FUNCTIONS Evaluating (Page 9 of 10)

To find the reference angle for a given trigonometric ratio, always use the absolute value of the ratio when evaluating the inverse trigonometric function. The result will be a positive angle whose terminal side will lie in Quadrant I. This reference angle can then be used to find other angles as needed.

For example, find an angle θ, 0 <= theta < 2pi, if the terminal side of θ lies in Quadrant II and tanθ = -0.2084. To find the reference angle, evaluate the arctangent function at 0.2084. Using the positive value will ensure that the result is a Quadrant I angle.

 CLEAR key.

 2nd inverse tangent key. 0.2084 Right parenthesis key. ENTER key.

 Calculator screen image.
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