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March 3, 2009

Square Root Day

Posted: 12:56 PM ET

[cnn-photo-caption image=

caption="Square Root Day celebrates perfect squares like these. How many more can you name?"]
For years I have been celebrating March 14 (3/14) as Pi Day, which I have always considered the mathematical holiday of the highest importance - I mean, come on, it's Albert Einstein's birthday! - and never thought about commemorating any other day for its numerical beauty.

But today, I have been out-geeked. Today, it turns out, is Square Root Day. That's because it's 3/3/09, and 3 x 3 = 9, meaning 3-squared equals 9. I had never considered that this relationship between month, day, and year occurs so rarely. In fact, this "square root" coincidence in dates only happens nine times every century - the last one being 2/2/04.

How should you celebrate Square Root Day? According to CNET, a teacher in Redwood City, California, has organized a contest. Apparently, people will cut root vegetables into squares or make foods into the square root symbol shape.

In addition, perhaps you can listen to the song by Huey Lewis and the News, "Hip to be Square."

For more on Square Root Day and other math holidays, check out the Cybrary Man Web site.

And, stay tuned for my Pi Day tips next weekend.

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Karl Blessing   March 3rd, 2009 2:24 pm ET

Yay, my birthday today was square root day. 😀

Ninth   March 3rd, 2009 2:55 pm ET

Shouldn't it be Happy Square Day? 3^2 = 9, but sqrt(9) = +/- 3, not just 3.

Courtney   March 3rd, 2009 3:04 pm ET

Today is a great day to celebrate...and it is Hip to be Square. Today is great squared for me (hehehehehehe) it is my 36th birthday!!!!! I am super geeked!!!!!

Karl Blessing   March 3rd, 2009 3:49 pm ET

@ninth... ok somewhere in the middle of the 3rd will be the square root of 9 😀

tina   March 3rd, 2009 4:30 pm ET

I've always said my birthday was easy to remember! It's (3^2)^2! That's 3/9/81. It is a true square birthday! and yes, it IS hip to be square! happy birthday courtney!

Mike   March 3rd, 2009 4:32 pm ET

Personally, as semi-cool is this day is, I really think it's a bad name. Sure, 3×3 = 9, but the date 03032009 CANNOT be taken a square root of and be a whole number.

It's an even bigger travesty, because 2009 is the only year this decade that has dates that you can take a square root of.

AND it happens twice.

AND it happens THURSDAY!!!!! (For those of us following American date conventions). I think there should be a big deal about this. I hope Elizabeth Landau writes something up about it for Thursday.

03052009 is a perfect square. When you take the square root of it, you get exactly 1747.

Also, no joke, April Fools this year can be taken a square root of. The square root of 04012009 is exactly 2003.

No more dates (after these two coming up shortly) until 2016!

Tim Coffey   March 3rd, 2009 4:38 pm ET

Only nine 'square root days' in a century?
If one considers the 100th year of any century – the one ending in '00' (and yes, the '00' years are the END of a century, not the beginning) - then 10/10/2100 would be the tenth such 'square root day' in this century.

Rocket scientist   March 3rd, 2009 4:55 pm ET

Actually the square root of 9 is only 3. +/- 3^2 equals 9. if you want the root to be -3 it would be an imaginary number. So effectively the root would actually be 3i

John Meakin   March 3rd, 2009 5:00 pm ET

For Pi day.

355/113 = Pi to better than 1 part in a million.

I wonder why ?

Blake   March 3rd, 2009 5:08 pm ET

For me, it is not only square root day today, but "Cubed Day" as well – I turn 27 today (3 x 3 x 3 = 27)! Weird!

aswensen   March 3rd, 2009 9:40 pm ET

Pi day 6 years from now will be the one time a century where we get 5 digits of pi (3/14/15).

Cyniq   March 3rd, 2009 10:18 pm ET

Let's see: 1/1/01, 2/2/04, 3/3/09, 4/4/16, 5/5/25, 6/6/36, 7/7/49, 8/8/64, 9/9/81/ 10/10/100. However, this would only be true in the 1st century CE. To carry on: 11/11/121, 12/12/144 and that's all there will ever be, a total of 12 actual square dates. Thankfully we missed these dire dates by around 19 centuries. Whew! Dropping the first two digits from the year yields only minor reasons to panic.

Tim   March 3rd, 2009 11:09 pm ET

Me and my wife, the two of us, were married on April 16th, 1988. How perfect is that? (and we've been married for twenty years.) Just sign me, fascinated with numbers. (Among many other things)

Mike   March 3rd, 2009 11:43 pm ET

I'm a graduate student in mathematics, and I'm getting married on Pi Day. Woohoo!

Bill   March 4th, 2009 5:48 am ET

Tom C's correction is only part of the story. There will also be additional 'square days' next century.

10×10 = 100 which will fit in 2100, but not 2200, 2300 etc

11 x 11 = 121 which should real excitementing in 2121. *OMFG* – 2121 is *another* square. Our cups runneth over !

12 x 12 = 144 which of course like 10×10 and 11×11, will only happen once per millenium. Now that's reason to celebrate BIG TIME!!!

Kinda' wants you to take better care of yourself so you can live to see those amazing days, doesn't it?

Franko   March 4th, 2009 5:51 am ET

March 14 (3/14) as Pi Day
3 from base 10; - to base 12 - then .14 base 10 to base 28-31 ?

Take all the letters in the Bible, divide by all the letters in the Quoran
If odd, then there is a Good God - if even then there is Good Grief

Colin   March 4th, 2009 1:11 pm ET

To the second poster: the square root of 9 is just 3, not +/- 3. It is true that (-3)^2 = 9, though. The reason for this is that "square root" is a function: and in mathematics, functions take one input and can give only ONE output.

janet jones   March 5th, 2009 12:18 am ET

square root of what exactly? what are we talking about here?

Adam   March 5th, 2009 12:30 pm ET

I'm a computer science major and I still think this guy is a nerd.

Franko   March 5th, 2009 11:34 pm ET

Equation x=2^0.5 solved for x - x = 8119/5741

What is the advantage of the fraction form ?

Tim Coffey   March 6th, 2009 9:50 am ET

Colin, congratulations – you've just discovered why y=sqrt(x) is not
a mathematical function, but y=x^2 is.

Franko   March 7th, 2009 12:53 am ET

f(x)=sqrt(x)=x^0.5 - Equation y=x^0.5 solved for y - y = sqrt(x)
sqrt is a function, like sin cos etc. x^2 - x^0.5
f(x)=x^2 is not 1-1 - but f(x)=x^0.5 is 1-1

Michael   March 13th, 2009 3:29 pm ET

The time between each "square root day" inreases by exactly two more years. 1/1/2001, 3 yrs later 2/2/2004, 5 yrs later 3/3/2009, 7 yrs later 4/4/2016, 9 yrs later 5/5/2025, 11 yrs later 6/6/2036, 13 yrs later 7/7/2049, 15 yrs later 8/8/2064, ...11/11/2121, 23 yrs later 12/12/2144, and then 25 yrs later 13/13/2169 (aka 1/13/2169) is opposite day. But everyone know that. Oh don't deny it, you know it.

Ken Mollohan   March 14th, 2009 11:27 pm ET

Here's the slickest formula I've found to approximate Pi:
[3*[1109377 / 1059377]] = 3.14159265304 ...

Easy to remember and original to me. Nine decimals isn't too bad.
Ken Mollohan

Franko   March 15th, 2009 4:19 pm ET

See wiki;
"quadrillionth (1,000,000,000,000,000:th) bit of π, which" = "0"
But we are digital, not bit people. - powers of 10 - not powers of 2

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