In the context of angles in standard position, the term ? is used to identify the reference point or angle.

• A. Coterminal angle
• B. Terminal side
• C. Quadrant
• D. Initial side

Answer: (D)

Verified step by step guidance

1. Understand the terminology related to angles in standard position: an angle in standard position has its vertex at the origin, its initial side along the positive x-axis, and its terminal side determined by the angle's measure.
2. Identify the 'initial side' as the fixed starting position of the angle, which is always along the positive x-axis in standard position.
3. Recognize that the 'terminal side' is the ray that rotates from the initial side to form the angle, and its position depends on the angle's measure.
4. Know that 'coterminal angles' are angles that share the same terminal side but differ by full rotations of 360 degrees (or \$2\pi$ radians).
5. Understand that 'quadrants' refer to the four sections of the coordinate plane divided by the x- and y-axes, which help describe the location of the terminal side.