1) (15x^2y^4)/(-y^5) = -15x^2/y
2) (a^2−9)/(ab+3b) = (a+3)(a-3)/(b(a+3)) = (a-3)/b
3) (x−4)/(20−5x) = -(4-x)/(5(x-4))
4) (a^3−c^3)/((a^2−c^2)(a^2+ac+c^2)) = (a-c)(a^2+ac+c^2)/((a-c)(a+c)(a^2+ac+c^2)) = 1/(a+c)
1) (15x^2y^4)/(-y^5) = -15x^2/y
2) (a^2−9)/(ab+3b) = (a+3)(a-3)/(b(a+3)) = (a-3)/b
3) (x−4)/(20−5x) = -(4-x)/(5(x-4))
4) (a^3−c^3)/((a^2−c^2)(a^2+ac+c^2)) = (a-c)(a^2+ac+c^2)/((a-c)(a+c)(a^2+ac+c^2)) = 1/(a+c)