At the moment...

Tuesday, May 20, 2008

All numbers are equal...say what?

I'm feeling mathematical today, I don't know exactly why. Anyway, here's a problem that's really interesting I found here.

If my students were paying attention to my discussions about methods of proof, my favorite topic in discrete math, I think they'll find this interesting, too.



All numbers are equal
Theorem: All numbers are equal.

Proof: Choose arbitrary a and b, and let t = a + b.
Then

a + b = t
(a + b)(a - b) = t(a - b)
a^2 - b^2 = ta - tb
a^2 - ta = b^2 - tb
a^2 - ta + (t^2)/4 = b^2 - tb + (t^2)/4
(a - t/2)^2 = (b - t/2)^2
a - t/2 = b - t/2
a = b

So all numbers are the same, and math is pointless.

Woah! What just happened here?
I hope some of my students will find this and tell me what exactly happened there. Haha. Cute, isn't it?

2 comments:

frix! said...

hmm... something's fishy fishy... the conclusion was a = b, therefore, by reverse engineering (ngek!), you can't multiply both sides of the equation by (a-b) kasi...

a = b
a - b = 0

so any number multiplied by 0, zero jud... rights? sorry nag-comment ko without permission... heheheh... ciao!

Em said...

hi frix,

ok ra kaayo magcomment oi...

it is not assumed that a = b. a and b are any real number.