Verified answer

1,28 = 128 x 10⁻² = 2⁷x10⁻²

puisque 2x2x2x2x2x2x2 = 128

on a donc

1,28 x 10⁻⁴ = (2⁷x10⁻²) x 10⁻⁴ = 2⁷x10⁻⁶

et comme  10 = 2x5

on aura  2⁷x(2x5)⁻⁶ = 2⁷x2⁻⁶x5⁻⁶ = 2 x 5⁻⁶