4/(3y) + 7/(9y) = 12/(9y) + 7/(9y) = 19/(9y) , D = { x ∈ℝ | x≠0}
(4y)/(3x) + y/(5x) = (20y)/(15x) + (3y)/(15x) = (23y)/(15x), D = {(x,y) ∈ℝ^2 | x ≠ 0}
8/(3x) - 5/( 9y) = (24y)/(9xy) - (5x)/(9xy) = (24y - 5x)/(9xy) , D = {(x,y) ∈ℝ^2 | (x * y ≠ 0}
4 - (3 + 6x)/(4x) = (16x)/(4x) - (3 + 6x)/(4x) = (-3 + 10x)/(4x) , D = { x∈ℝ | x≠0}
Bitte selbst nachrechnen und allfällige Korrekturen melden.