x ×y = ( 2xy - 6x ) + (- 6y +18 ) + 3 = 2x( y- 3 ) - 6( y- 3) + 3=
= ( y- 3) ·( 2x -3) + 3 = 2· ( y- 3) ·( x -3) +3
b. x×x = 2· ( x-3)·( x-3) +3= 2· ( x-3 )² +3
2· ( x -3 ) ² +3= 11
2·( x-3)² = 8
( x-3)²= 4 ⇒ x-3=2 ; x₁=5
x-3 =- 2 ; x₂= -1 nu verifica
c. √1 ×√2×√3 ×.. ×√9 ×.... ×√2009 = 3
↓
obs. ca x ×√9 = x ×3 = 2·( x -3) · ( 3 - 3) + 3 = 0 + 3 = 3
pentru orice valoare a lui x ; legea x×3 = 3