See the figure below. so in an standard position, the vertex of the angle called (B) is on the origin (0, 0) of the x and y axis. Therefore, one side of the angle is always fixed along the positive x-axis, namely, going to the right along the axis in the 3 o'clock direction (see line BC in the figure). This is called the initial side of the angle.The other side of the angle is called the terminal side.
So, in the subsequent figures you can see each angle drawn. Then, the angles that match the figure above are the measures of the angle. That is:
-450°
-90°
270°
