From GeoGebra Manual
- DynamicCoordinates[ Point A, Number X, Number Y ]
- creates a point with coords (X, Y). This point is dependent, but can be moved. Whenever you try to move the new point to coordinates (x,y), point A is moved there and coordinates for the new point are calculated. Works best if point A is not visible. At least one of X and Y should depend on A.
- B DynamicCoordinates[A,round(x(A)),round(y(A))]. You try to move B to (1.3,2.1) using the Move Tool. Point A becomes (1.3,2.1) and B appears at (1,2). Create three slider a, b, and c with an interval from 0 to 1.
- B DynamicCoordinates[A,x(A),min(y(A),sin(x(A)))] create a point under under sin(x).
Note: PointIn[y<sin(x)] is easier solution in this case.