Salut !
1) A = 8/9 - 15/9 × 5/6
= 8/9 - (15×5)/(9×6)
= (8×6)/(9×6) - (15×5)/(9×6)
= (48-75)/54
= -27/54
= -27/(2×27)
= -1/2
2) B = 49 × 10³ × 6 × 10⁻¹⁰ ÷ 14 × 10⁻²
= 294 × 10³⁻¹⁰ ÷ 14 × 10⁻²
= 294 ÷ 14 × 10³⁻¹⁰⁺²
= 21 × 10⁻⁵
= 2,1 × 10⁻⁴
3) 406 ÷ 2 = 203
203 ÷ 7 = 29
donc : 406 = 2 × 7 × 29
696 ÷ 2 = 348
348 ÷ 2 = 174
174 ÷ 2 = 87
87 ÷ 3 = 29
donc : 696 = 2³ × 3 × 29
donc : 406/696 = (2 × 7 × 29) / (2³ × 3 × 29)
= 7/(2²×3)
= 7/12
