Respuesta :

a5904640

We need to know that:

[tex]\frac{a}{b}-\frac{c}{d}=\frac{a.d-b.c}{b.d}[/tex]

[tex]\frac{a}{2}-\frac{1}{2}=\frac{a.2-2.1}{2.2}=\frac{2a-2}{4}=\frac{a-1}{2}[/tex]