You can imagine the wave being a circle.
The highest point on the unit circle would have the y value of 1 and since that's a quarter of a circle past, it would have a x value of pi/2
Henceforth, the first answer would be (pi/2, 1)
Taking the same before analogy, the point would be in the middle of the circle therefore it would have the y value of 0.
Since it completed a half of the circle's circumference, it would have the x value of pi.
Henceforth, the second answer would be (pi, 0)
:D
