If angle $\mathrm{gfd}$ is in standard position and its terminal side lies along the positive $y$-axis, what is its measure?

• A. $80°$
• B. $50°$
• C. $40°$
• D. $90°$

Answer: (D)

Verified step by step guidance

1. Recall that an angle in standard position has its vertex at the origin and its initial side along the positive x-axis.
2. Understand that the terminal side of the angle is the ray that rotates from the initial side to the angle's position.
3. Recognize that if the terminal side lies along the positive y-axis, the angle corresponds to a quarter turn from the positive x-axis.
4. Since a quarter turn in the counterclockwise direction corresponds to 90 degrees, the angle measure is 90°.
5. Therefore, the measure of angle \( gfd \) in standard position with its terminal side on the positive y-axis is \( 90^\circ \).