Question

Să se arate că (x+2) – 9x -18=(x-1)(x+2)(x+5) ​

Answer 1

$\it (x+2)^3-9x-18=(x+2)^3-9(x+2)=(x+2)[(x+2)^2-3^2]=\\ \\ =(x+2)[(x+2-3)(x+2+3)]=(x+2)(x-1)(x+5)=(x-1)(x+2)(x+5)$