How does 2 + 2 = 5?

Question

I know it can be done. I saw it done many years ago.

Something like 1+1+1+1=5, .5+.5+1+1+1=5 then the .5's are rounded up and you get 5

Answer 1

I'll give you a proof:

Start with the identity:
-20 = -20

Express both sides in slightly different, yet equivalent ways:
16 - 36 = 25 - 45

Factor both sides:
4^2 - 4 x 9 = 5^2 - 5 x 9

Complete the square by adding 81/4 to both sides:
4^2 - 4 x 9 + 81/4 = 5^2 - 5 x 9 + 81/4

Factor both sides again:
( 4 - 9/2 )^2 = ( 5 - 9/2 )^2

Take the square root of both sides:
4 - 9/2 = 5 - 9/2

Cancel the common factor:
4 = 5

And since 2 + 2 = 4:
2 + 2 = 5

Q.E.D. (But obviously there is an error in my proof... can you find it?) This probably isn't the "proof" you were looking for, but it does show 2 + 2 = 5...

Edit: Okay there was a request to know where the error lies. It's in the step where we take the square root of both sides. Note that (x)^2 = (-x)^2, but the square root of both sides is not necessarily equal.

Answer 2

No, no rounding up is required.

Here's how it works: (p.s. I gave this proof to five people already)

Take two constants, a and b. Take them to be 2, for instance.

Now, multiply both sides by b:
ab = b²
Subtract a² from both sides:
ab - a² = b² - a²
Factor both sides:
a(b-a) = (b+a)(b-a)
Divide both sides by (b-a):
a = a+b
Now, subtract a from both sides:
0 = b
Therefore:
0 = 2
Now, if you multiply both sides by 2.5 at this point, you get:
0 = 5
So, 2+2=5, which is true, because 0+0=0. Get my logic?

P.S. This proof is... not EXACTLY accurate. There's something wrong with it. It's the part where you divide by (b-a). This equals zero, and you can't exactly divide by zero...

Ok, bandf, I give up. You've hidden your error quite well. What is it?

Answer 3

ive never seen a 2+2=5 proof, but i do know the 1=0 proof, and that only works b/c the constant of integration is left out

Answer 4

Steven F is Right, and that is one of the reasons you cant divide by zero. There are some things in math that just aren't allowed.

It just like logic. lets say there are a group of kids. They vote on whether 2+2=5

23 vote yes

7 vote no

does this make it logically true? No, this is known as appealing to the majority, and is a logical fallacy.

Same with math. You saw that proof because someone did an illegal operation in their logical thinking of math.

:-)

-Nick

Answer 5

there is an unknown # that is 1 and makes it 5

Answer 6

"2" is a symbol that can stand for any amount. It's like a variable. We just use it to stand for the value of two. Suppose we replace "2" with x and solve

2 + 2 = 5
x + x = 5
2x = 5
x = 2.5

So yes it is possible if the symbol "2" stands for the amount of "two and one-half"

Answer 7

Start with a=b.
Some where onlng the ling divide by (a-b).
Prove a=2b.
Since a=b, this porves 1=2.
Division by 0 (a-b) is undefined.
You can prove anything.
I forgot the rest.

Answer 8

You'd have to have other numbers though wouldnt you? It can't just be 2+2=5. You need other numbers or signs or something.

Strange.. but pretty cool.

Answer 9

The second 2 is pregnant. Look closely. She's starting to show.

Answer 10

It can't be done. People who do this crap are just very tricky. Math does not lie.