Bonsoir,
A = 9/7- 2/5 * 15/8
= 9/7- (2*15)/(5*8)
= 9/7- (30)/40
= 9/7- 3/4
= (9*4)/(7*4)- (3*7)/4*7
= 36/28-21/28
= (36-21)/28
= 15/28
B = 6*10^-7 *15*10¹¹ / 8*(10²)⁴
=
[tex](6 \times 10 {}^{ - 7 + 11} \times 15) \div (8 \times 10 {}^{2 \times 4} )[/tex]
= (6 * 10 ⁴ * 15) / (8*10^8)
= 90 / 8 * 10⁴/10^8
= 11.25 * 10-⁴
= 1.125 * 10 * 10-⁴
= 1.125 *10-³ écriture scientifique
= 0.001125 écriture décimale
