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4-71.

Find all values of from where the following equations are true. Sketching a picture of the unit circle may help.

  1. Circle with horizontal diameter, points in first & second quadrants, each about 1 third up from respective diameter endpoints, horizontal segment between points, radii to the points, each a hypotenuse of right triangle, with horizontal legs on x axis, vertical leg on each labeled 1 half, central angle from positive x axis to first quadrant radius labeled 30 degrees, and central angle from positive x axis to second quadrant radius labeled 150 degrees.


  1. Circle with point in second quadrant, about 2 thirds up from right diameter endpoint, right triangle with hypotenuse between center & point, horizontal leg on negative x axis, labeled negative 1 half, a reflection of the triangle across the x axis, places a second right triangle with bottom vertex in third quadrant, central angle from positive x axis, to second quadrant radius labeled 120 degrees, central angle from positive x axis, to third quadrant radius labeled 240 degrees.

  1. What special angle(s) are involved?
    What does the negative sign mean?

  1. These angles are coterminal with the -axis.

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