bonsoir
a = 2/7 - 3/7 x 21/9
a = 2/7 - 63/63
a = 18/63 - 63/63
a = - 45/63 = - 5/7
b = 10 ⁶ x 6 x 10 ⁻³ sur 15 x 10⁴
b = 6 x 10 ³ sur 15 x 10 ⁴
b = 0.4 x 10 ⁻¹
c = ( 3/5 - 1/4) : ( 1/3 + 2)
c = ( 12/20 - 5/20) : ( 1/3 + 6/3
c = 7/20 : 7/3
c = 7/20 x 3/7 = 21/140 = 3/20