Answer:
[tex]\sf \dfrac{\pi}{2}[/tex]
Step-by-step explanation:
Angles are measured in a counterclockwise direction from the positive x-axis (initial side).
Therefore, if an angle's terminal side is on the positive y-axis, the angle will be 90° or [tex]\sf \dfrac{\pi}{2}[/tex] radians.
See attached diagram for visual explanation.
If the angle was [tex]\pi[/tex] then the terminal side would be on the negative x-axis.
If the angle was [tex]\dfrac32\pi[/tex] then the terminal side would be on the negative y-axis.
If the angle was [tex]2\pi[/tex] then the terminal side would be on the positive x-axis and the angle would be one complete revolution of the circle.
