Off by one character

Posted on 26 April 2018 by John

There was a discussion on Twitter today about a mistake calculus students make:

$\frac{d}{dx}e^x = x e^{x-1}$

I pointed out that it’s only off by one character:

$\frac{d}{de}e^x = x e^{x-1}$

The first equation is simply wrong. The second is correct, but a gross violation of convention, using x as a constant and e as a variable.

3 thoughts on “Off by one character”

Imneversure

26 April 2018 at 22:05

It’s wrong by one letter another way.
$\frac{d}{dx}e^x=e\,e^{x-1} \{=e^x\}$
Jeff Wood

27 April 2018 at 07:52

Very neat. Which Twitter feed originated the discussion?
Many thanks
Jeff
John

28 April 2018 at 07:36

Jeff: this tweet

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