Bonjour,
Factoriser:
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. 9x*2-81-2x(3x-9)=(3x-9)(3x+9) -2x(3x-9)= (3x-9)(3x+9-2x)= (3x-9)(x+9)
= 3(x-3)(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)= - 2(x-4)(x-1)
D. x(2x+1)-6x-3= x(2x+1)- 3(2x+1)= (2x+1)(x-3)
