Multiply $a^4x^3$ by $ \dfrac{y}{a^2} $ to get $ \dfrac{ a^4x^3y }{ a^2 } $.

Step 1: Write $ a^4x^3 $ as a fraction by putting $ \color{red}{1} $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} a^4x^3 \cdot \frac{y}{a^2} & \xlongequal{\text{Step 1}} \frac{a^4x^3}{\color{red}{1}} \cdot \frac{y}{a^2} \xlongequal{\text{Step 2}} \frac{ a^4x^3 \cdot y }{ 1 \cdot a^2 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ a^4x^3y }{ a^2 } \end{aligned} $$

Multiply $ \dfrac{a^4x^3y}{a^2} $ by $ x $ to get $ \dfrac{ a^4x^4y }{ a^2 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{a^4x^3y}{a^2} \cdot x & \xlongequal{\text{Step 1}} \frac{a^4x^3y}{a^2} \cdot \frac{x}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ a^4x^3y \cdot x }{ a^2 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ a^4x^4y }{ a^2 } \end{aligned} $$

Multiply $ \dfrac{a^4x^4y}{a^2} $ by $ y^3 $ to get $ \dfrac{ a^4x^4y^4 }{ a^2 } $.

Step 1: Write $ y^3 $ as a fraction by putting $ \color{red}{ 1 } $ in the denominator.

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{a^4x^4y}{a^2} \cdot y^3 & \xlongequal{\text{Step 1}} \frac{a^4x^4y}{a^2} \cdot \frac{y^3}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ a^4x^4y \cdot y^3 }{ a^2 \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ a^4x^4y^4 }{ a^2 } \end{aligned} $$