Répondre :
a) A = (2x+1)(5x-3)-(2x+1)
A = 2x*5x +2x*-3 + 5x-3 -2x-1 (* est multiplié par)
A = 10x² -6x +5x -2x -4
A = 10x² -3x-4
b) x= -1
A = 10x²-3x-4
A = 10*(-1)² -3*-1 -4
A = 10+3-4
A = 9
x=1/3
A = 10x²-3x-4
A = 10(1/3)² -3*1/3 - 4
A = 10/9 -4
A = 10/9 -36/9
A = 26/9
A = 2x*5x +2x*-3 + 5x-3 -2x-1 (* est multiplié par)
A = 10x² -6x +5x -2x -4
A = 10x² -3x-4
b) x= -1
A = 10x²-3x-4
A = 10*(-1)² -3*-1 -4
A = 10+3-4
A = 9
x=1/3
A = 10x²-3x-4
A = 10(1/3)² -3*1/3 - 4
A = 10/9 -4
A = 10/9 -36/9
A = 26/9