w e b l i n k 
Math Shirts
(31 Dec 2003 at 13:11) 
I am thinking of opening up a little internet tshirt store. In my searches on the internet I found math novelty tshirts, some of which are groaningly funny. If you're a math nerd. 


...and you believe in real numbers. 
I didn't see anything noncomputable there! 
But do you really believe in integration? 
Sure, as long as the functions are continuously differentiable. 
The quadratic formula is the only one I know by heart.
But I haven't the faintest idea what can be done by using it...
Not that it matters. I haven't needed it ever since I last had to use it during math class. 
Tuuur, quick! Solve this algebraic equation for x!
3x^2 + 8x = 5

Aaaaaargh!!! I don't know how!!!
:) 
Use the quadratic formula! 
But... but... I REALLY don't know how!!!
I don't see any a or b or c in that equation!
:)
(and yes, I know, I am a hopeless case) 
Haha, that's great that you bothered to memorize the quadratic formula but not what the inputs are. ;)
(FYI a is the coefficient of x^2, 3 in the above, b the coefficient of x (8), and c the constant (5)). 
Lemme see... ehm...
so that's 8, plus or minus (I'll never understand why that doesn't matter, it's quite a difference) square root (is that how you say it in english? In dutch it's 'wortel') 64 minus 4 times 15, divided by 6...
(writes frantically)
Hmmm, according to my computations, x would be 1!
Wow!!! That's the first time since 1984 that I actually USED the quadratic formula to solve an equation!
Thanks!
(insert triumphant trumpet sounds here) 
Hehe. Well, I think you got a minus sign wrong somewhere because 3(1)^1  8(1) is 5, not 5. The actual answer is much less nice, because it has a square root of 124 instead of 4. But that's the right idea!
The reason that there's a plusorminus in there is that quadratic equations (ones with x^2) are parabolas when graphed. That means that they might cross the xaxis twice:
\ /
\ /

\ /
~ ~
`___ '
(That probably won't come out, oh well...)
So the quadratic equation has two solutions, one on the right side (plus) and one on the left (or minus). In the case that the square root is 0, then the tip of the parabola just touches the x axis at a single point. If b^24ac is negative, then the square root doesn't exist, and that's the case that the parabola lives entirely above the x axis and never touches it at all.

Oh, the diagram is terrible! It's visible in the page source. (Alas, I have nobody to blame but myself...) 
The shirts are are all horrible. I did like the comment on the log shirt though. But seriously, what's so fucking special about the quadratic formula? I guess it's the most complicated thing that kids in high school these days have to memorize. I would probably buy a shirt with various representations (NOT approximations) of pi. Or how about the first few members of the busy beaver sequence? Caption: On one side, "Get busy." On the other, "Got beaver?" 
I thought of more obscure tshirts as well. But your target audience would be so small! 
The audience for my busy beaver shirt is small? But computation affects us all! Plus, it's all about the captions. 
Also please use scare quotes when referring to the busy beaver "function" or "sequence". 
Teri Shivo needs the Quadratic equation. 
Yes, all I could find were shirts like that. Bring on the obscure shirts! 

