Primary Trigonometric Ratios, Given an Angle in Standard Position

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Primary Trigonometric Ratios, Given an Angle in Standard Position

Given any angle in standard position, you can calculate the primary trigonometric ratios by first calculating the reference angle. Using the reference angle, you can determine the positive value of each trigonometric ratio. In the Investigation, you may have noticed that the quadrant in which an angle in standard position terminates defines whether a particular trigonometric ratio is positive or negative. The signs of the trigonometric ratios are different in each quadrant because of the signs of the \(x\)- and \(y\)-coordinates in each quadrant. To determine if the ratio should be positive or negative, use the CAST rule.