I'm working as a long-term substitute for 3 math classes. Yesterday I gave students a very basic graphing problem. A cheese pizza costs $5; each topping is $1. I was looking for a y intercept of 5.
Some kids started their y axis at 5, though. As long as it's labeled, I see this as misleading but not necessarily wrong. I gave them credit but made them fix it. They were arguing with me about it, which is a good thing, but I told them we were using the graph to communicate and that this was too misleading.
Is there any convention that says Cartesian coordinates have to start with 0? Does a graph have to start at the origin? When I see those corners drawn, I assume we're at (0,0). I know that sometimes graphs are misleading on purpose, and that's an excellent lesson to students. But there are other students in the class who might benefit more from being told, "That's wrong; the correct answer looks like this." Just like we tell 5-year-olds that "c" makes a "k" sound. It's misleading, but you deal with the subtleties later.
Some kids started their y axis at 5, though. As long as it's labeled, I see this as misleading but not necessarily wrong. I gave them credit but made them fix it. They were arguing with me about it, which is a good thing, but I told them we were using the graph to communicate and that this was too misleading.
Is there any convention that says Cartesian coordinates have to start with 0? Does a graph have to start at the origin? When I see those corners drawn, I assume we're at (0,0). I know that sometimes graphs are misleading on purpose, and that's an excellent lesson to students. But there are other students in the class who might benefit more from being told, "That's wrong; the correct answer looks like this." Just like we tell 5-year-olds that "c" makes a "k" sound. It's misleading, but you deal with the subtleties later.
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