Verified Answer :

  • The angle \(\theta = -\frac{5\pi}{6}\) radians is converted to degrees: \(\theta = -\frac{5\pi}{6} \times \frac{180^\circ}{\pi} = -150^\circ\).
  • The negative sign indicates a clockwise rotation starting from the positive x-axis.
  • Rotating \(150^\circ\) clockwise from the positive x-axis places the terminal side in the third quadrant, specifically \(30^\circ\) below the negative x-axis.
  • The angle corresponds to a positive rotation of \(210^\circ\), which is in the \(\boxed{\text{third quadrant}}\).

Explanation

  1. Convert radians to degrees.

The angle given is \(-\frac{5\pi}{6}\) radians. In standard position, an angle's vertex is at the origin \((0,0)\), and its initial side is the positive x-axis. A positive measure indicates a counterclockwise rotation, while a negative measure indicates a clockwise rotation.

To convert \(-\frac{5\pi}{6}\) radians to degrees, we multiply by \(\frac{180^\circ}{\pi}\):
\[-\frac{5\pi}{6} \times \frac{180^\circ}{\pi} = -5 \times 30^\circ = -150^\circ\]
This means the terminal side of the angle is rotated \(150^\circ\) clockwise from the positive x-axis.

  1. Locate the terminal side position.

The positive x-axis is at \(0^\circ\). Rotating \(150^\circ\) clockwise:

  • After \(90^\circ\) of clockwise rotation, the terminal side aligns with the negative y-axis (\(-90^\circ\)).
  • Continuing another \(60^\circ\) clockwise (\(150^\circ - 90^\circ = 60^\circ\)), the terminal side lands in the third quadrant.
  • Specifically, the negative x-axis is at \(-180^\circ\). The angle \(-150^\circ\) is \(30^\circ\) above the negative x-axis (since \(-150^\circ = -180^\circ + 30^\circ\)).
  • Equivalently, in a positive sense, \(-150^\circ\) is equal to \(360^\circ - 150^\circ = 210^\circ\). An angle of \(210^\circ\) is \(30^\circ\) into the third quadrant past the negative x-axis.
  1. Conclusion.

The angle \(-\frac{5\pi}{6}\) radian in standard position:

  • Starts at the positive x-axis.
  • Rotates clockwise by \(150^\circ\).
  • Terminates in the third quadrant, forming an angle of \(30^\circ\) with the negative x-axis.

The final answer is that the angle lies in the third quadrant. \(\boxed{\text{third quadrant}}\).

Examples

Understanding standard position is essential in fields like navigation and mechanical engineering. For instance, if a radar system tracks an object at an angle of \(-\frac{5\pi}{6}\) radians, the operator knows the object is in the third quadrant relative to their north-south (y-axis) and east-west (x-axis) reference lines. Calculating this helps the operator identify the object's general direction quickly.