salut SVP aider moi! !!je comprends pas

a =-1/3 +5/3(-2/5)³ 
  =-1/3 +5/3(-8/125)
  =-1/3 +5/3(-8/25×5)
  =-1/3 -8/75
  = -25-8/75 = -33/75 
b=2-³ +4/3 ÷(-2)³ = 1/2³ +4/3 ×(-2)³ = 1/8 -4/24 = 3-4/24 =-1/24 
c= -3²+9(1/3-1)² 
  = 9 +9(1/3 -3/3)²
  = 9+ 9(-2/3)² 
  = 9+9(4/9)
  =9+ 36/9 =9+4  =13