3. Вычислите: a) $$\frac{68^2 - 12^2}{96^2 - 16^2}$$; б) $$\frac{13^2 + 30 \cdot 13 + 15^2}{14 \cdot 40 - 14 \cdot 12}$$

3. Вычислите: a) $$\frac{68^2 - 12^2}{96^2 - 16^2} = \frac{(68 - 12)(68 + 12)}{(96 - 16)(96 + 16)} = \frac{56 \cdot 80}{80 \cdot 112} = \frac{56}{112} = \frac{1}{2}$$ б) $$\frac{13^2 + 30 \cdot 13 + 15^2}{14 \cdot 40 - 14 \cdot 12} = \frac{13^2 + 2 \cdot 15 \cdot 13 + 15^2}{14(40 - 12)} = \frac{(13 + 15)^2}{14 \cdot 28} = \frac{28^2}{14 \cdot 28} = \frac{28}{14} = 2$$