Question

a/2 - 1/2 and please explain!!

Answer 1

We need to know that:

$\frac{a}{b}-\frac{c}{d}=\frac{a.d-b.c}{b.d}$

$\frac{a}{2}-\frac{1}{2}=\frac{a.2-2.1}{2.2}=\frac{2a-2}{4}=\frac{a-1}{2}$