Comment on peut arriver de 2x-5/4-× = 5/2 à -30+9×/8-2× = 0 ?

(2x-5) / (4-x) = 5/2
((2x-5) / (4-x)) - 5/2 = 0
((2x-5)2 / (4-x)2) - (5(4-x) / 2(4-x)) = 0
((4x-10) / (8-2x)) - ((20-5x) / (8-2x)) = 0
(4x-10-20+5x) / (8-2x) = 0
(-30+9x) / (8-2x) = 0