Thin convex lens: O: The boject I: The image C: The optical center F: The principal focus F': The principal focus in front of the mirror How to use: Adjust the point O to move the object. Adjust the height of the object by the slider.
Try to create a formula between object distance and image distance. (You can use similar triangles.) Try to create a formula between their heights. If the object is located uF in front of the mirror, if u/(u-1) > 0, the image is located [u/(u-1)]F behind the mirror, if u/(u-1) < 0, the image is located -[u/(u-1)]F in front of the mirror.