Next we need to throw away the slope-intercept form and use the line equation instead. [Click here](https://www.khanacademy.org/math/algebra2/functions_and_graphs/undefined_indeterminate/v/why-zero-divided-by-zero-is-undefined-indeterminate) to see why dividing by zero is bad. [Click here](https://www.khanacademy.org/pixar/ray-tracing-in-2d/6147153693900800) to try the interactive program show
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