SVG and JavaScript
One of my high school students enjoyed drawing these geometric figures. The lower edge approximates a parabola as the number of lines increases. We were studying conic sections in the class. We made this web app that automates the process of drawing the figure. The original app used text boxes for input, but I made the interface easier to use.
Note that this automation helps students see the parabola, but it prevents the students from experiencing the more tactile pencil drawing part of the exercise, which can be relaxing. So automating a task like this may not always be the best strategy for student learning.
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