12/5/13 — Happy Right Triangle Day!

Happy Right Triangle Day!  Today we celebrate a favorite geometric object:  the 5-12-13 right triangle.

5-12-13 Triangle blue

Of course, the sides of this triangle satisfy

5^2 + 12^2 = 13^2

and, thus, form a right triangle.  But one reason I like this particular right triangle so much is the role it plays in another favorite triangle.  The 5-12-13 triangle fits together perfectly with the 9-12-15 right triangle

5-12-13 plus 9-12-15 Triangle blue

to make the 13-14-15 triangle!

13-14-15 triangle blue

The 13-14-15 triangle is special in its own right:  it is a Heronian triangle, a triangle with rational side lengths and rational area.  In fact, this triangle has  integer side lengths and integer area, making it especially interesting!

Happy Right Triangle Day!  If you’re in New York City, you might want to join the Museum of Math as they pythagorize the Flatiron Building!

12/03/2013 — Happy Permutation Day!

Today we celebrate a Permutation Day!  I call days like today permutation days because the digits of the day and month can be rearranged to form the year.

12032013Not only is today a permutation day, but it is also a double-transposition day!  We can turn the month and day into the year by first transposing the ‘1’ and the ‘2’, and then transposing the ‘1’ and the ‘0’.  Permutation days are also nice because, unlike Palindrome days, they can celebrated on both sides of the Atlantic without heated disagreement.

As usual on Permutation Days, I suggest celebrating by mixing things up!

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