If an angle in standard position has its terminal side along the positive $y$-axis, what is its measure in degrees?

• A. $180°$
• B. $270°$
• C. $90°$
• D. $45°$

Answer: (C)

Verified step by step guidance

1. Recall that an angle in standard position is measured starting from the positive x-axis and rotating counterclockwise.
2. Identify the positive y-axis as the line where the terminal side of the angle lies.
3. Understand that the positive y-axis corresponds to a 90-degree rotation from the positive x-axis.
4. Therefore, the measure of the angle whose terminal side lies along the positive y-axis is 90 degrees.
5. Verify that this angle is one of the common reference angles on the coordinate plane: 0° on positive x-axis, 90° on positive y-axis, 180° on negative x-axis, and 270° on negative y-axis.