Bonjour,
a. (x - 1)(2x + 5)+4x² + 20x + 25
= (x-1) (2x+5) +(2x+5) ²
= (2x+5) ( x-1 +2x+5)
= (2x+5) ( 3x +4)
b. 9x² - 81–2x(3x –9)
= (3x-9)(3x+9) - 2x(3x –9)
= (3x-9) (3x+9 -2x)
=(3x -9) ( x+9)
c. 5x – 20-(2x+3)(x-4)
5(x-4) -(2x+3)(x-4)
= (x-4) ( 5 -2x -3)
=(x-4) ( -2x +2)
d. x(2x + 1)- 6x-3
= x(2x+1) - 3( 2x +1)
= (2x+1) ( x- 3)
