Radius of the inscribed circle of a right angled triangle


For that “About An Inscribed Circle” problem I posted the other day: HowardAt58 worked out one way of proving what the radius of the circle that just fits within the 5-12-13 right triangle has to be, and in a pretty neat geometric fashion. Worth the read. I recommend following his steps along by hand, writing each out, but that reflects that I’m much more likely to follow mathematical reasoning if I write it out, even if I don’t do something past what the original author does. HowardAt58 also includes a little conjecture, inspired by playing around with a couple of Pythagorean triangles (playing around with a couple of examples is a great way to find conjectures), which I at least believe to be true.

Interestingly, his proof isn’t the same geometric proof that I’d realized we could do, so, I’m thinking to include that as another follow-up around here when I can make a couple diagrams that explain it.

Saving school math

incircle radius with text

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