Double-click the matrix A twice in the algebra window, then you can change the matrix elements. Move the points A, B, C in the left window. You can see the transformed triangle by the matrix A in the right window. Move the points A', B', C', D' in the right window. You can see the transformed quadrilateral by the inverse matrix of A in the left window. Move the "move" point in the left window. It will be transformed in the right window by the given matrix A. * If you want to change the numbers of the polygons, find and double-click "polygon1" and "polygon2" in the algebra window.