In the figure, DE is drawn parallel to BC. Click and drag any of the blue points to change the shape and orientation of the triangle ABC.

- Given that DE is parallel to BC, what can be said of <ABC and <ADE? What other angles are equal?
- What can be said of triangles ABC and ADE?
- What is the effect on the ratios of corresponding sides when the point D is moved? Why is this so?
- What is the effect on the ratios of corresponding sides when either of the points A, B and C are moved? Why is this so?