Me either. I mean, yeh, it's true because that's what areas do. If the shapes are similar then the sides are in proportion in terms of their lengths and the areas are in proportion in terms of the squares of the lengths. So really they should just do A1/A2=b^2/e^2. dunno why they did the rest. Yeh, it's confusing.
I'm not following how they're getting from:
http://math.stackexchange.com/questions ... a-questionFor two similar triangles, the ratio of the height of the first triangle to the height of the second triangle is equal to the ratio of the base of the first triangle to the base of the second triangle.