Finding cumulative distribution function, given density function using integration

I am trying to find the cumulative distribution function given the following density function: $$f_X(x)=
frac{2}{3sqrt{x}}, &0leq x < frac{9}{16}\
0, &text{otherwise.}

I know I need to integrate $f_X(x)$ to find $F_X(x)$ but I am unsure what the initial value for this integral must be. Would this be correct integral, $intlimits_{0}^{x}f_X(x)dx=frac{4sqrt{x}}{3}=F_X(x)$?