1. $\frac{2a^2}{a+1} \div \frac{a^2-a}{a^2-1} =$

2. $\frac{5x^2-25x}{x^2-7x+10} \times \frac{x^2-4}{15x^2} =$

3. $\frac{x+4}{3x^2-12x} \div \frac{x^2+8x+16}{x^2-4x} =$

4. $\text{ب: } \frac{6x^2-6}{x-6} \div \frac{x^2+7x+6}{x^2-36} =$

5. $\frac{10x}{x^2} \times \frac{x^2-2x}{5x^2} =$