It's carnival time again! The 37th Carnival of Mathematics is now up at Logic Nest. They're taking additional submissions through Sunday evening, too, so if you missed out on getting your post included you still have time, and if you already read the Carnival you should check back for more math.

Here's a cute little geometric factoid that has something to do with one of the posts over at the 33rd Carnival of Mathematics. I'll leave it as a puzzle which post it belongs to...

Let ABC be any triangle in the Euclidean plane, and AD be any line. Form points A', B', and C' as the perpendicular projections of A onto BC, B onto AD, and C onto AD respectively. Then triangles ABC and A'B'C' are similar.

( diagram )

(Hint: in the post I have in mind, ABC is isosceles and A' is the midpoint of BC.)

Jeff Shallit takes his turn at posting Carnival of Mathematics #31.

30th Carnival of Mathematics, now up at The Number Warrior.

Carnival of Mathematics #23: Haiku Edition. From The Math Less Traveled.

22nd Carnival of Mathematics, from Wild About Math!

Carnival of mathematics #21: bar-hopping at last. From the not-so-secret-anymore blogging seminar.

19th Carnival of Spam Mathematics, from Good Math, Bad Math. Baseball, personal finance, romance, and personal improvement. Or maybe, statistics, number theory, algebra, and math education.

Carnival of Mathematics 18, from JD2718. He seems to have made quite an effort to dig up relevant posts: as he says, "it's kind of big..."

Seventeenth Carnival of Mathematics, now up at MathNotations.

The 16th Carnival of Mathematics is now up at Learning Computation. From it we learn that secondary-school mathematics is good, research mathematics is bad, and computer science is ugly. Well, but there are significantly more research math (and vaguely computational research math) links than the previous few of these, so that's good.

Math Carnival 10. With a bit of side discussion over whether it's appropriate to continue lumping elementary and advanced math together, or whether any split should wait until there's enough more volume.

Carnival of Mathematics IX: this time it's alphabetical.

The eighth Carnival of Mathematics, now up on Suresh's geomblog.

The seventh carnival of mathematics, now up at nOnoscience.

The sixth carnival of mathematics, now up at Modulo Errors.

Fifth Carnival of Mathematics, now up at Science and Reason. More focused on recent mathematical news (Paul Cohen, medieval islamic Penrose tiles, and E₈) and less on a catch-all of popular math blog posts than previous carnivals, but it still has some of the latter type of posts as well.

The Fourth Carnival of Mathematics is up!

It's Friday, and it's two weeks after the last Carnival of Mathematics, so it must be carnival time again! Michi hosts the third carnival of mathematics.

The second carnival of mathematics is here. Good Math, Bad Math has some fun working all the links into a story.

For future carnivals, there's also a convenient submission form.