It goes like this:
x(square root of 5x-1) - (square root of 5x-1)
They are like terms now. Is it something like this:
x - (square root of 5x-1) ?
Actually, what you're going to do is factor the $\displaystyle \sqrt{5x-1}$ out of the equation, what you do is:
1. Pull the $\displaystyle \sqrt{5x-1}$ out by adding parentheses around the entire equation and tacking a $\displaystyle \sqrt{5x-1}$ right before the first parenthesis:
Original:
$\displaystyle x\sqrt{5x-1} - \sqrt{5x-1}$
Step 1:
$\displaystyle \sqrt{5x-1}(x\sqrt{5x-1} - \sqrt{5x-1})$
2. Inside the parentheses, you divide each term by $\displaystyle \sqrt{5x-1}$:
Step 1:
$\displaystyle \sqrt{5x-1}(x\sqrt{5x-1} - \sqrt{5x-1})$
Step 2:
$\displaystyle \sqrt{5x-1}(x - 1)$
And with that, you are done.