Multiply $ \color{blue}{2} $ by $ \left( cirw+1\right) $ $$ \color{blue}{2} \cdot \left( cirw+1\right) = 2cirw+2 $$

Multiply $ \color{blue}{2} $ by $ \left( cirw+1\right) $ $$ \color{blue}{2} \cdot \left( cirw+1\right) = 2cirw+2 $$

Multiply $ \color{blue}{2} $ by $ \left( cirw+1\right) $ $$ \color{blue}{2} \cdot \left( cirw+1\right) = 2cirw+2 $$

Multiply $ciw$ by $ \dfrac{r}{2cirw+2} $ to get $ \dfrac{ cirw }{ 2cirw+2 } $.

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

Step 2: Multiply numerators and denominators.

Step 3: Simplify numerator and denominator.

$$ \begin{aligned} ciw \cdot \frac{r}{2cirw+2} & \xlongequal{\text{Step 1}} \frac{ciw}{\color{red}{1}} \cdot \frac{r}{2cirw+2} \xlongequal{\text{Step 2}} \frac{ ciw \cdot r }{ 1 \cdot \left( 2cirw+2 \right) } = \\[1ex] & \xlongequal{\text{Step 3}} \frac{ cirw }{ 2cirw+2 } \end{aligned} $$

Subtract $ \dfrac{cirw}{2cirw+2} $ from $ \dfrac{1}{2cirw+2} $ to get $ \dfrac{-cirw+1}{2cirw+2} $.

To subtract expressions with the same denominators, we subtract the numerators and write the result over the common denominator.

$$ \begin{aligned} \frac{1}{2cirw+2} - \frac{cirw}{2cirw+2} & = \frac{1}{\color{blue}{2cirw+2}} - \frac{cirw}{\color{blue}{2cirw+2}} = \\[1ex] &=\frac{ 1 - cirw }{ \color{blue}{ 2cirw+2 }}= \frac{-cirw+1}{2cirw+2} \end{aligned} $$