Salut! svp aidez moi pour le 2 =) (19 pts)

bonjour

a ) 7/15 - 2/15 x ( 11/4 - 1/2)
a = 7/15 - 2/15 x ( 11/4 - 2/4)
a = 7/15 - 2/15 * 9/4
a = 7/15 - 18/60
a = 28/60 - 18/60
a = 10/60 = 1/6

b = ( - 16) x 10 ⁻³ x 25 x ( 10²)³ sur 5 x 10 ⁵ x 4 x 10 ⁻³
b = - 400 x 10 ⁻³ x 10 ⁶ sur 20 x 10 ²
b =  - 400 x 10 ³ sur 20 x 10 ²
b = - 20 x 10 
b = - 200
b = - 2 x 10²

c = 5/7 + 1/7 x ( 10/2 + 1/2)
c = 5/7 + 1/7 * 11/2
b = 5/7 + 11/14
b = 10/14 + 11/14
b = 21/14 = 1.5