Câu 7
a) 4x(5$x^{2}$ +2x-1) = 20$x^{3}$ +8$x^{2}$ -4x
b) $(x-3y)^{2}$ = $x^{2}$ -6xy+9$y^{2}$
c) (3$x^{2}$ $y^{2}$ -6$x^{2}$ $y^{3}$ +12xy) : 3xy = xy-2x$y^{2}$ +4
d)( $x^{3}$ -3$x^{2}$ + 5x - 6 ) : ( $x^{2}$ - x + 3)
= [( $x^{3}$ -$x^{2}$ +3x ) - ( 2$x^{2}$ - 2x + 6 )] : ( $x^{2}$ - x + 3)
= [x( $x^{2}$ - x + 3) - 2( $x^{2}$ - x + 3 )] : ( $x^{2}$ - x + 3)
= ( x - 2 )( $x^{2}$ - x + 3 ) : ( $x^{2}$ - x + 3)
= x - 2
Câu 8
a) $x^{2}$ - $y^{2}$ - 3x + 3y = ( $x^{2}$ - $y^{2}$ ) -( 3x - 3y )
= ( x - y )( x + y ) - 3( x - y )
= ( x - y )( x + y - 3 )
b) $x^{2}$ - 5x + 6 = $x^{2}$ -2x - 3x + 6
= ( $x^{2}$ - 2x ) - (3x - 6 )
= x( x - 2 ) - 3( x - 2 )
= ( x - 3 )( x - 2 )
