Multiply $ \dfrac{1+insx}{c} $ by $ o $ to get $ \dfrac{inosx+o}{c} $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{1+insx}{c} \cdot o & \xlongequal{\text{Step 1}} \frac{1+insx}{c} \cdot \frac{o}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ \left( 1+insx \right) \cdot o }{ c \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ o+inosx }{ c } = \frac{inosx+o}{c} \end{aligned} $$

Multiply $ \dfrac{inosx+o}{c} $ by $ s $ to get $ \dfrac{ inos^2x+os }{ c } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} \frac{inosx+o}{c} \cdot s & \xlongequal{\text{Step 1}} \frac{inosx+o}{c} \cdot \frac{s}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ \left( inosx+o \right) \cdot s }{ c \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ inos^2x+os }{ c } \end{aligned} $$

Multiply $ \dfrac{inos^2x+os}{c} $ by $ x $ to get $ \dfrac{ inos^2x^2+osx }{ c } $.

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.

$$ \begin{aligned} \frac{inos^2x+os}{c} \cdot x & \xlongequal{\text{Step 1}} \frac{inos^2x+os}{c} \cdot \frac{x}{\color{red}{1}} \xlongequal{\text{Step 2}} \frac{ \left( inos^2x+os \right) \cdot x }{ c \cdot 1 } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ inos^2x^2+osx }{ c } \end{aligned} $$