Subtract $ \dfrac{x}{y} $ from $ x $ to get $ \dfrac{ \color{purple}{ xy-x } }{ y }$.

Step 1: Write $ x $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: To subtract raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the first fraction by $\color{blue}{ y }$.

$$ \begin{aligned} x- \frac{x}{y} & \xlongequal{\text{Step 1}} \frac{x}{\color{red}{1}} - \frac{x}{y} = \frac{ x \cdot \color{blue}{ y }}{ 1 \cdot \color{blue}{ y }} - \frac{ x }{ y } = \\[1ex] & \xlongequal{\text{Step 2}} \frac{ \color{purple}{ xy } }{ y } - \frac{ \color{purple}{ x } }{ y }=\frac{ \color{purple}{ xy-x } }{ y } \end{aligned} $$