Quadrantal Angle

Definition

A quadrantal angle is an angle that measures a specific fraction of a full circle, typically one of the four 90-degree angles formed by the coordinate axes. These angles are important in the study of trigonometry and the unit circle.

5 Must Know Facts For Your Next Test

1. Quadrantal angles are always multiples of 90 degrees, such as 0°, 90°, 180°, and 270°.
2. The four quadrantal angles divide the coordinate plane into four equal quadrants, each spanning 90 degrees.
3. Quadrantal angles are often used to simplify trigonometric calculations, as the sine, cosine, and tangent functions have special values at these angles.
4. Angles in the first quadrant (0° to 90°) are considered positive, while angles in the second, third, and fourth quadrants are negative.
5. Quadrantal angles are important in the study of the unit circle, which is a circular representation of the trigonometric functions.

Review Questions

• Explain the relationship between quadrantal angles and the coordinate plane.
  • Quadrantal angles are closely tied to the coordinate plane, as they define the four 90-degree quadrants that divide the plane. The four quadrantal angles of 0°, 90°, 180°, and 270° create the axes of the coordinate plane, with each quadrant spanning 90 degrees. This allows for the simplification of trigonometric calculations and the study of the unit circle, which is centered on the coordinate plane.
• Describe the special properties of the trigonometric functions at quadrantal angles.
  • At quadrantal angles, the trigonometric functions (sine, cosine, and tangent) have special values that make calculations easier. For example, at 0° and 360°, the sine is 0, the cosine is 1, and the tangent is 0. At 90°, the sine is 1, the cosine is 0, and the tangent is undefined. These special values allow for the simplification of trigonometric expressions and the use of the unit circle to visualize and understand the behavior of the trigonometric functions.
• Analyze the significance of quadrantal angles in the context of the unit circle and their applications in trigonometry.
  • Quadrantal angles are fundamental to the unit circle, which is a circular representation of the trigonometric functions. The unit circle is centered on the coordinate plane, with the four quadrantal angles (0°, 90°, 180°, and 270°) defining the axes. This allows for the easy visualization and understanding of the periodic nature of the trigonometric functions, as well as their special values at these key angles. In trigonometry, quadrantal angles are often used to simplify calculations and solve problems, as the trigonometric functions have known, easily-manipulated values at these angles. The understanding of quadrantal angles is crucial for success in topics such as the unit circle, trigonometric identities, and solving trigonometric equations.

Related terms

Acute Angle: An angle that measures less than 90 degrees.

Obtuse Angle: An angle that measures more than 90 degrees but less than 180 degrees.

Coterminal Angles: Angles that have the same terminal side, differing by a multiple of 360 degrees.