Question

Descompuneti in factori expresiile urmatoare utilizand, eventual, identitatile
$x^{2}$ - (a+b)x + ab = (x-a) (x-b) sau $x^{2}$ + (a+b)x + ab = (x+a) (x+b)
a) $x^{2}$ + 6x + 8
b) $x^{2}$ - 10x + 9

Answer 1

x² + 2x + 4x + 8  =x· ( x + 2) + 4·( x +2) = ( x +2) ·( x +4) 
x² -x - 9x + 9 = x·( x -1)  - 9 ·( x -1) = ( x -1 ) ·( x - 9) 

Answer 2

a)
=x²+(2+4)x+2·4=(x+2)(x+4)

b)=x²-(9+1)x+9·1=(x-9)(x-1)