# Math Help - Intergral help

1. ## Intergral help

Over what open interval does the formula F(x)=[int (from 1 to x) dt/t]

represent an antiderivative of f(x)=1/x? and find a point where the graph of F crosses the x-axis.

I don't even how to start calculating this problem.

Thank you

2. Originally Posted by noppawit
Over what open interval does the formula F(x)=[int (from 1 to x) dt/t]

represent an antiderivative of f(x)=1/x? and find a point where the graph of F crosses the x-axis.

I don't even how to start calculating this problem.

Thank you
hmm, since you are already in the integrals, you should already know the function for which you differentiate it gives $\frac{1}{x}$.

let $F(x) = \ln x$. Then $F'(x) = \frac{1}{x}$.

Thus, by FTOC, $F(x) = \int_a^x \frac{1}{t} \, dt$, where $a>0$..