A = (x+5)(x+4)
x × x + x × 4 + 5 × x + 5 × 4
[tex]x^{2}[/tex] + 4x + 5x + 20
[tex]x^{2}[/tex] + 9x + 20
B = (2x+1)(x+7)
2x × x + 2x × 7 + 1 × x + 1 × 7
[tex]2x^{2}[/tex] + 14x + x + 7
[tex]2x^{2}[/tex] + 15x + 7
C = (x+6)(3x-4)
x × 3x + x × (-4) + 6 × 3x + 6 × (-4)
[tex]3x^{2}[/tex] - 4x + 18x - 24
[tex]3x^{2}[/tex] + 14x - 24
D = (2x-5)(3x+1)
2x × 3x + 2x × 1 - 5 × 3x - 5 × 1
[tex]6x^{2}[/tex] + 2x - 15x - 5
[tex]6x^{2}[/tex] - 13x - 5