Pythagorean Theorem Follow-Up: Solution

Monday I asked my students to determine whether this triangle was equilateral, isosceles, or scalene, and to prove their answer.  The hint is in the post title: this is a Pythagorean Theorem activity.  Here is the original triangle:


If you said “isosceles,” you’re correct!  Here’s the proof, using Pythagoras’s Theorem.


The hypotenuse of the right triangle, shown in red, is 5 units — the same as the base of the original triangle.  Therefore the triangle has two congruent sides and is isosceles!

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