Bonjour !

Exercice 5:

1) L = 42 + 35x = 6*7 + 5*7 * x = 7(6 + 5x)

M = 55x² - 33 = 11*5 *x² - 11*3 = 11(5x² - 3)

N = 27x - 21x² = 3x * 9 - 3x * 7x = 3(9 - 7x)

2) P = 7 - 2x - 18 + 10x = -11 + 8x

Q = 5x - 3x² - 11 + 10x² - 7 = 5x + 7x² - 18

3) P = 5x + x+3 + 10x - 0.5 + 7x + 1 + x+3 = 24x + 6.5

Exercice 6:

R = (2x + 1)(x + 7) = 2x*x + 2x*7 + 1*x + 1*7 = 2x² + 14x + x + 7 = 2x² + 15x + 7

S = (x + 6)(3x - 4) = x*3x - x*4 + 6*3x - 6*4 = 3x² - 4x + 18x - 24 = 3x² + 14x - 24

T = (8x - 5)(-9x + 1) = 8x*(-9x) + 8x*1 - 5*(-9x) - 5 *1 = -72x² + 8x + 45x - 5 = -72x² + 53x - 5

Exercice 7:

1) x = 0

U = 0² - 4*0 + 3 = 0 - 0 + 3 = 3

V = (3-0)(0+1) = 3*1 = 3

x = 3

U = 3² - 4*3 + 3 = 9 - 12 + 3 = 0

V = (3-3)(3+1) = 0*4 = 0

2) U = x² - 4x + 3

V = (3-x)(x+1) = 3*x + 3*1 - x*x -x*1 = -x² + 2x + 3

Donc les expressions U et V ne sont pas égales.

Voilà, j'espère t'avoir aidé.