If an angle $tsu$ is in standard position and its terminal side passes through the point $(0,1)$ on the unit circle, what is the measure of angle $tsu$ in degrees?

• A. $25°$
• B. $45°$
• C. $90°$
• D. $65°$

Answer: (C)

Verified step by step guidance

1. Understand that the angle \( tsu \) is in standard position, meaning its vertex is at the origin and its initial side lies along the positive x-axis.
2. Recognize that the terminal side of the angle passes through the point \( (0, 1) \) on the unit circle, which means the radius vector from the origin to this point has length 1.
3. Recall that points on the unit circle correspond to angles where the coordinates are \( (\cos \theta, \sin \theta) \). Here, \( \cos tsu = 0 \) and \( \sin tsu = 1 \).
4. Identify the angle \( tsu \) whose cosine is 0 and sine is 1. This corresponds to the angle where the terminal side points straight up along the positive y-axis.
5. Conclude that the measure of angle \( tsu \) in degrees is \( 90^\circ \), since this is the angle where the terminal side passes through \( (0, 1) \) on the unit circle.