Individually, I would have the students plot the original triangle on their graph, then multiply the coordinates by 2, plot the new points. In partners, use the worksheet to talk about the similarities and differences of what they just did. Then I, or a student, could demonstrate what we should be seeing on an overhead for the class. I would ask questions to compare how the coordinating points relate to the origin on the coordinate graph. Then do the same thing with the pentagon, individually plot the points for the original figure, multiply each point by ½, then with a partner finish the questions on the worksheet. As a class, have a different student or group present the graphing on an overhead. Again, look at how it correlates to the origin.
The following questions would be good classroom discussion and/or journal entries. I would ask questions to compare the original coordinates to the coordinates to the dilated figures. Did the shapes change? How are they the same/different? What would happen if we multiplied the original figure by 3, or ¼, will your figures enlarge or shrink? Explain your reasoning. How does if effect the relationship to the origin? What do you notice about the distance from the origin to the 2 coordinating points of the figures?
At first, students might assume side length and angle measure will change in dilation. But as you start comparing, you can explore the idea of similarity. The students can cut out the figures to compare, side lengths change but the angle measure stays the same. This is also a good way to confirm that no matter what size of triangle, pentagon, or any polygon, the angle sum of that particular figure will always be the same. Students might also ask how small or large you can dilate a figure. They can experiment with numbers with a partner until they come up with an answer, infinity both ways, and be able to explain their reasoning.