0
votes
7answers
464 views

What is wrong in this proof?

\begin{align*} \frac{0}{0} &= \frac{100-100}{100-100} \\ &= \frac{10^2-10^2}{10(10-10)} \\ &= \frac{(10+10)(10-10)}{10(10-10)} \\ &= \frac{10+10}{10} \\ &= \frac{20}{10} \\ &= ...
2
votes
1answer
83 views

Can there be a real solution to the square root of -1? [duplicate]

Basically what the title says: Can there be a real solution to the square root of $-1$ (or any negative number in fact) or is it defined to be unreal? Because of this: $$ \begin{align} \sqrt{-1} ...
1
vote
2answers
112 views

Calculation of bucks missing

Lets say I bought 1000 bucks from a friend of mine and 500 bucks from another.Now I went to the market and there I accidentally lost 1000 bucks. Ok then I did some shopping which costs me 300 bucks. ...
4
votes
1answer
2k views

Expense and Balance Mismatch

I searched and couldn't find a post in stack exchange for this. I recently saw a calculation for rupee spend and having balance in yahoo, but i am not quiet convinced with the answer given... the ...
1
vote
4answers
200 views

How do I explain the fallacy $\frac00=2$ in this case?

$$ \begin{align} \frac00 &= \frac{x^2-x^2}{x^2-x^2}\\ &= \frac{(x-x)(x+x)}{x(x-x)}\\ &= \frac{x+x}x\\ &= 2 \end{align} $$ Thus $\frac00=2$ How do I explain this fallacy?
0
votes
1answer
26 views

mean of two consecutive number helps proving both number equals.. [duplicate]

Well i was wondering how is this possible. let say: 4=4 -> R.H.S =4-(9/2)+(9/2) =sqrt( (4 - ( 9/2 )) ^ 2)+ (9/2) =sqrt( 16 - 36 +( 9/2 )^2)+ (9/2) =sqrt( - 20 +( 9/2 )^2)+ (9/2) =sqrt( -45 ...
5
votes
3answers
208 views

Starting with $\frac{-1}{1}=\frac{1}{-1}$ and taking square root: proves $1=-1$

In this blog post, RJ. Lipton mentions an example of common mathematical traps. In particular, that ``square root is not a function''. He shows the following trap: Start with: ...
3
votes
3answers
284 views

$1 +1$ is $0$ ?​ [duplicate]

Possible Duplicate: -1 is not 1, so where is the mistake? $i^2$ why is it $-1$ when you can show it is $1$? So: $$ \begin{align} 1+1 &= 1 + \sqrt{1} \\ &= 1 + \sqrt{1 ...
4
votes
5answers
803 views

The $3 = 2$ trick on Google+

I found out this on Google+ yesterday and I was thinking about what's the trick. Can you tell? How can you prove $3=2$? This seems to be an anomaly or whatever you call in mathematics. Or ...
32
votes
7answers
1k views

Bad Fraction Reduction That Actually Works

$$\frac{16}{64}=\frac{1\rlap{/}6}{\rlap{/}64}=\frac{1}{4}$$ This is certainly not a correct technique for reducing fractions to lowest terms, but it happens to work in this case, and I believe there ...
22
votes
6answers
2k views

$-1$ is not $ 1$, so where is the mistake?

I know there must be something unmathematical in the following but I don't know where it is: \begin{align} \sqrt{-1} &= i \\ \\ \frac1{\sqrt{-1}} &= \frac1i \\ \\ \frac{\sqrt1}{\sqrt{-1}} ...