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Unit circle and obtuse angles

This test uses the unit circle to determine trigonometric values. Tasks cover quadrants, signs of sine and cosine, obtuse and supplementary angles and checking whether a resulting value is reasonable.

Questions: 10Estimated time: 14 minutes
Unit circle and obtuse angles
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Sample questions

  1. Give the unit-circle point coordinates for angle ___°.
  2. Simplify sin(180° − ___°).
  3. Simplify cos(180° − ___°).
  4. Simplify tan(180° − ___°).
  5. An acute angle α has sine ___. What is sin(180° − α)?

Unit circle and obtuse angles

On the unit circle, the point corresponding to angle α has coordinates (cos α, sin α). Thus sine is the y-coordinate, cosine the x-coordinate, and tan α = sin α / cos α whenever cos α ≠ 0.

Signs and reference angles

In quadrant II, sine is positive while cosine and tangent are negative. Reference angles give values such as sin(180° − α) = sin α and cos(180° − α) = −cos α. Determine the quadrant before choosing a sign.

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