for math fans

[joannaingram84]

I am a big fan of math, specifically algebra up to college algebra. I love the formulas. One of my favorites is the quadratic formula, x equals -b plus or minus the square root of b squared minus 4ac over c. What are your favorite formulas?

[candyterrius]

The Pythagorean Theorem a2 + b2 = c2. I'm not much a fan for math. 

[lvstephanie]

Mine wasn't actually a formula, but rather a "proof" that 2=1... It was given to our class in 6th grade, I think, as an example of how a mathematical proof was written. The teacher also said she'd give anyone a bunch of extra credit if they could find the fault in the proof... Sadly, no one figured it out. I still like how often it fools even people that are good at math (see if I can write it here...):

Proof that 2=1 given x=y

x=y       Given
x²=xy    Multiply by x
x²-y²=xy-y²   Subtract by y²
(x+y)(x-y)=y(x-y)   Factoring
x+y=y   Divide by (x-y)
y+y=y   Substitute y for x (Since it was given x=y)
2y=y     Add
2=1      Divide by y (QED)

What people fail to see is that since x=y, then x-y=0 and thus the step where you divide both sides of the equation by (x-y), you are actually dividing by 0, which is a mathematical error. Thus from that point on, the proof is false.