$\displaystyle \frac{a-b}{2} \cdot \sqrt{3}$\displaystyle \frac{a-b}{2} \cdot \sqrt{3}

$\displaystyle \frac{a-b}{6} \cdot \sqrt{3}$\displaystyle \frac{a-b}{6} \cdot \sqrt{3}

$\displaystyle \frac{a+b}{2}$\displaystyle \frac{a+b}{2}

$\displaystyle \frac{a+b}{4}$\displaystyle \frac{a+b}{4}