1. ## Dubious Derivative

If you can spot the error please do not post the explanation let other people have fun solving it. For the first few days. If you do and I see it I will delete it.

Notice that $\displaystyle x^2=x+x+x...+x$ where $\displaystyle x$ appears $\displaystyle x$ times. Thus, taking the derivative of both sides,
$\displaystyle 2x=1+1+1...+1$ but 1 appears $\displaystyle x$ times thus, $\displaystyle 2x=x$? What is wrong?

2. My lips are sealed, unless we're allowed to post our guess in a 'spoiler' kind of tag? Unvisible unless selected.

Perhaps another one, spot the error but don't reveal (or reveal covered using white text in a code box for example).

$\displaystyle e^{2\pi i} = 1 \Leftrightarrow \ln e^{2\pi i} = \ln 1 \Leftrightarrow 2\pi i = 0$

3. TD! Your problem is connected with my "paradox" I posed here before.

How did you like the derivative problem?

4. What's the background color used by these boards? We can use it as invisible ink.

5. Originally Posted by Treadstone 71
What's the background color used by these boards? We can use it as invisible ink.
I do not know exactly but you can use MS-Paint. They have a color-picker. It is a tools which shows your EXACTLY which color something is.

6. Originally Posted by ThePerfectHacker
I do not know exactly but you can use MS-Paint. They have a color-picker. It is a tools which shows your EXACTLY which color something is.
RGB values 245,245,255 apparently.

RonL

7. Originally Posted by ThePerfectHacker
TD! Your problem is connected with my "paradox" I posed here before.

How did you like the derivative problem?
Indeed!

I've seen the derivative fallacy before

8. Hex values are F5F5FF. Click on "quote" to see the exact tags.

9. ## white is almost invisible

If you right in white then [you can barely see it] unless you highlight between the brackets.

10. I'll have to remember this as an annoying "proof" of 2=1. I like it!

-Dan