Hello and welcome to FMH!

I've moved and re-titled the thread since this problem has nothing to do with calculus/differential equations. Which of the following is correct?

\(\displaystyle f(x)=\frac{x-3}{2x}\)

\(\displaystyle f(x)=x-\frac{3}{2x}\)

\(\displaystyle f(x)=x-\frac{3}{2}x\)