trigonometry

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(a) If è is in standard position, then the reference angle è is the acute angle formed by the terminal side of è and the ---Select--- x-axis y-axis . So the reference angle for è = 120°
is è = ?°, and that for è = 210°is è = ? degrees.

(b) If è is any angle, the value of a trigonometric function of è is the same, except possibly for sign, as the value of the trigonometric function of
è. So sin(120°) = sin ?°, and sin(210°) = −sin ?°.

  • trigonometry -

    the reference angle is to the X (or -x) axis

    for 120 it would be 180 - 120 = 60 degrees above x axis
    cos 60 = 1/2
    cos 120 = -1/2

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