1. [math]\frac{-4ab}{21c}\cdot\frac{14c^2}{18a^2}[/math]
2. [math]\frac{\left(cd\right)^3}{a}\cdot\frac{ax^2}{xc^2d}[/math]
3. [math]\frac{\left(3a\right)^3}{18b^3}\cdot\frac{12a^4b^5}{\left(3a\right)^2}[/math]
4. [math]\left(\frac{x^2}{y}\right)^{^2}\cdot\frac{5}{3x}[/math]
4. [math]\frac{4x+40}{3x}\cdot\frac{9x}{3x+30}[/math]
5. [math]\frac{4y^2-9}{4y^2}\cdot\frac{8y}{2y-3}[/math]
6. [math]\frac{x^2-y^2}{y^2}\cdot\frac{y^3}{y-x}[/math]
7. [math]-\frac{x^2-y^2}{x+y}\cdot\frac{1}{x-y}[/math]
8. [math]\frac{x^2-y^2}{x+y}\cdot\frac{11}{x-y}[/math]
9. [math]\frac{\left(y-2\right)^2}{\left(x-4\right)^2}\cdot\frac{x-4}{y-2}[/math]
10. [math]\frac{x^2+3x-10}{x^2+8x+15}\cdot\frac{x^2+5x+6}{x^2+4x+4}[/math]
11. [math]\frac{a^3-b^3}{a+b}\cdot\frac{a^2-b^2}{a^2+ab+b^2}[/math]
12. [math]\frac{y^2-y-12}{y+12}\cdot\frac{y^2-4y-12}{y-4}[/math]