Did You Know That… 2=1?

No, this is not a commercial of any kind (trying to convince you that if you buy 1 you will get 2)! This is just a mathematical proof that 2=1. I remember that my math teacher in high school first showed me this. I was quite impressed! A few days ago I randomly encountered the proof and recalled it. Here it is:

X = Y
X*X = Y*X                 ; Multiply by X
X*X-Y*Y = Y*X-Y*Y         ; Subtract Y*Y from both sides
(X-Y)*(X+Y) = Y*(X-Y)     ; Some standard conversions
X+Y = Y                   ; Cancel out (X-Y)
2*X = X                   ; Use that X = Y
2 = 1                     ; Divide both sides by X

Are you convinced now? 😉

  • Sam

    You just showed the stupid things that can happen when you divide by zero…

  • Valentin

    You are completely right. On the other hand I remember the first time I saw that as a child. I was quite impressed, because I was not able to figure it out!

    I think this is a good way to increase the interest of the children in math. To show them, that if they don’t understand math, they could be easily tricked 😉

  • Sam

    I guess that is true 🙂