Bonjour !
A = (3x+1)(5x+3) = 3x*5x + 3x*3 + 1*5x + 1*3 = 15x²+9x+5x+3 = 15x² + 14x + 3
B = 4(2x+1)(-x+3) = (8x+2)(-x+3) = 8x*(-x)+8x*3+2*(-x)+2*3 = -8x² +24x-2x-6 = -8x² +22x -6
C = (5x-3)² + (4 - 9x²) = 25x² - 30x + 9 + 4 - 9x² = 16x²-30x +13
D = (2x + 1) -(6x - 1)(3x + 8) = 2x + 1 - 18x² - 48x + 3x +8 = -18x² - 43x + 9
Voilà !
