2) \frac{a-2}{a^2} \cdot \frac{ab-a}{a-2} + \frac{2-b}{2a};

$$\frac{a-2}{a^2} \cdot \frac{ab-a}{a-2} + \frac{2-b}{2a} = \frac{a-2}{a^2} \cdot \frac{a(b-1)}{a-2} + \frac{2-b}{2a} = \frac{b-1}{a} + \frac{2-b}{2a} = \frac{2(b-1) + 2-b}{2a} = \frac{2b-2+2-b}{2a} = \frac{b}{2a}$$