Bonjour,
(1/2 - 3/4) × 4/9 = (2/4 - 3/4) × 4/9
= -1/4 × 4/9
= -4/36
= -1/9
1/2 - 3/4 ÷ 4/9 = 1/2 - (3/4 ÷ 9/4)
= 1/2 - (3/4 × 4/9)
= 1/2 - 12/36
= 18/36 - 12/36
= 6/36
= 1/6