Hello

it is correct to write:

$\displaystyle \int^x_0 f(x)\,dx$

or i need write ?

$\displaystyle \int^x_0 f(t)\,dt$

Mr F says: This is the one you want.
why ?

Mr F says: Let me re-write your two choices and then you tell me which one **doesn't** make sense: $\displaystyle {\color{red}\int^{x = x}_{x = 0} f(x)\,dx}$ $\displaystyle {\color{red}\int^{t = x}_{t = 0} f(t)\,dt}$
The question is :

if I need a substitution of f(x) in a formula :

$\displaystyle f(x)=sin(x)$

$\displaystyle y=f(x) + \int^x_0 f(x)\,dx $

I can directly replace f(x)

otherwise :

$\displaystyle y=f(x) + \int^x_0 f(t)\,dt $

don't seem me elegant imho..

Thanks for the possible answers !