Divide Rational Expressions

Simplify the rational expressions:

1. $\dfrac{x}{x^2}\div \dfrac{x}{x^2}$
2. $\dfrac{x}{3x}\div \dfrac{x}{2x}$
3. $\dfrac{x+1}{x^2}\div \dfrac{x+1}{7x}$
4. $\dfrac{9x}{3x^2+6x+9}\div \dfrac{x^2}{3x^2-27}$
5. $\dfrac{2x-2}{7x^2+14x}\div \dfrac{2x}{x+2}$
6. $\dfrac{x^2-5x-24}{x^2+2x+1}\div \dfrac{x^2-8x}{x+1}$
7. $\dfrac{9x}{x^2+4x-21}\div \dfrac{3x^2+9x}{x^2}$
8. $\dfrac{x^3-3x^2-10x}{x^2+5x-36}\div \dfrac{10x}{x^2+7x-18}$