2+2=5

Anyone know how to prove this to be true(even though it's not). A math teacher proved it to my math class. Everything made sense and no one could find the falacy.

Originally posted by smw6869
Anyone know how to prove this to be true(even though it's not). A math teacher proved it to my math class. Everything made sense and no one could find the falacy.

If there is a general formula involved in the proof, make sure division by zero isn't happening because that isn't allowed. So for example the classic case of the fallacy of 1=2 (which is very similar to yours)
step 1
Let a = b
step 2 Multiply both sides by a:
aa = ab
step 3 which is the same as:
a^2 = ab ( "a squared equals a times b" )
step 4 Add the quantity ( a^2 - 2ab) to both sides:
a^2 + (a^2 - 2ab) = ab + (a^2 - 2ab)
step 5 simplifying both sides we get:
(a^2 + a^2) - 2ab = a^2 + (ab - 2ab)
2(a^2) - 2ab = a^2 - ab
2 (a^2 - ab) = a^2 - ab
step 6 divide both sides by (a^2 - ab):
2(a^2 - ab) / (a^2 - ab) = (a^2 - ab) / (a^2 -ab)
step 7 cancel out like terms in num.&denom:
2 = 1 !!!

Two equals one? Impossible! What's the catch? The catch is, our very first assumption is Let a= b, and if that's true then the quantity (a^2 - ab) = (a^2 - a^2) = 0, and we are not allowed to divide by zero which is what we do in our "proof" in step 6. The proof is not allowed. No division by zero.

I bet this is the trick that is happening in your false proof of 2+2=5.

(sorry for all the edits, but I had to work out some formatting issues)

Great

This is generally to do with rounding:
2.4 rounds to 2
2.4+2.4=4.8 which rounds to 5.

If you round everything: 2+2=5

An alternative to this one I came across is this...

2+2=10

This is mathematically true, and breaks no rules, but I've left out one piece of information. What's the information I've left out?

Originally posted by agryson
An alternative to this one I came across is this...

2+2=10

This is mathematically true, and breaks no rules, but I've left out one piece of information. What's the information I've left out?

base 4

Originally posted by Mephisto2
base 4

Got it. Though when i was told it, the dumbass mixed them up and said
2+2=5... in base four. I slapped him over the back of the head.

How about 10+10=100

binary

but 10 x 10 = 100 is less clear 😵

6+5=3 anyone?

mod 8

no its not, if it's binary then it would either be 10 + 10 = 4 or 10 = 10 = 256; all depends where the other six zeros are

how about 8+8=15...

anyone who's a musician should get that

Originally posted by eatmybishop
no its not, if it's binary then it would either be 10 + 10 = 4 or 10 = 10 = 256; all depends where the other six zeros are

In binary there is no '4' or '256'

10+10=100 is quite correct (ie 2+2=4 in decimal)

10x10=100 is true in any base.

Originally posted by wolfgang59
In binary there is no '4' or '256'

10+10=100 is quite correct (ie 2+2=4 in decimal)

10x10=100 is true in any base.

no its not, you're wrong...

i was under the impression is was binary to decimal.. so you're right there, there is no 4 or 256 in binary... however you're still wrong...

in binary, it would be 10+10=10... you are wrong to say 100, its not, 1 + 1 = 1 or 0 + 1 = 1, 0 + 0 = 0.... there is no additional digit.... mr dumb!