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N°19
a= ax+2a
b = -3a-12
c = 3x 5ax
d = 2ab 2b²
e= 2x²+6x
f=-3y²-15y
g = -2x^3-15y  (^ = puissance)
h = 35y²+14y^4

N°20
a = 3x +2 +14+8x = 11x +16
b = 4x+9-42+6x = 10x -33

N°21
a= 5x+7-24-15x = -10x-17
b = -7x+3+18-9x = -16x +21