Differentiate an equation

1. Nov 13, 2011

fluidistic

My friend came up with the following:
$2x=1 \Rightarrow \frac{d}{dx}(2x)=\frac{d}{dx}1 \Rightarrow 2=0$. Shamefully I do not see what's wrong with this reasoning!
Can someone help me? :)

2. Nov 13, 2011

LCKurtz

2x=1 is not an identity. It is only true for x = 1/2.

3. Nov 13, 2011

fluidistic

Thank you LcKurtz, that makes sense.