x +x+1+x+2 = 138
3x = 138 -3
3x = 135
x = 45
x +x+40+x+40+220 = 1 440
3x = 1440 -40-40-220
3x = 1440 - 300
3x = 1140
x = 380
dans celle ci, tu as 2 signes = il y en a un de trop.
(x-12)(x+20)= x²
x²+20x -12x-240 = x²
x²-x² +20x -12x = 240
8x = 240
x = 30
