I have an assignment

> 
> Find an equation for a tangent line to the curve $y=e^x$ which also goes through the origin.
> 
> 
> 

However, in my formula it is asserted 
that the slope between at a point "p" and the origin is 

$m=\frac{e^p-0}{p-o}$ = $\frac{d}{dx}e^x$ **(at $x=p$)** = $e^p$

but surely $\frac{e^p-0}{p-o} = \frac{e^p}{p}$ how is this equal to 

$\frac{d}{dx}e^x$ **(at $x=p$)** = $e^p$?

Am I missing something obvious?

Thank you in advance