Réponse:
[tex](x + 1)(x + 4) = x \times x + x \times 4 + 1 \times x + 1 \times 4 = {x}^{2} + 4x + x + 4 = {x}^{2} + 5x + 4[/tex]
[tex]c = ( x + 1)(4 - x) = x \times 4 - x \times x + 1 \times 4 - 1 \times x = 4x - {x}^{2} + 4 - x = -4x - {x}^{2} + 4 - x = - {x}^{2} + 3x + 4[/tex]
[tex]( x - 1)(x + 4) = x \times x + x \times 4 - 1 \times x - 1 \times 4 = {x}^{2} + 4x - x - 4 = {x}^{2} + 3x - 4[/tex]
[tex](x - 1)(x - 4) = x \times x - 4 \times x - 1 \times x +4 \times 1 = {x}^{2} - 4x - x + 4 = {x}^{2} - 5x + 4[/tex]
