α

Point represents y-coordinate of point B vs. angle α.

SINE WAVE
Use slider to change the value of α.
Use COMMAND-Z to erase the trace.

α = 0.5235987755982988 rad (slider from 0 to 360°, step °)
A = Point(xAxis)
c = Circle(A, 1)
M, D = Intersect(c, xAxis)
B = Rotate(D, α, A)
β = Angle(D, A, B)
a = Ray(A, B)
S: (α, y(B))
b = OrthogonalLine(B, xAxis)
C = Intersect(b, xAxis)
d = Segment(B, C)