E. 3X2 – 3XY – 5X + 5Y F. 3X2 + 6XY + 3Y2 – 3 Z2 = (3X2 – 3XY ) –...

4 ) - DE CUONG ON THI TOAN 8 HK1 CO DAP AN
Toán DE CUONG ON THI TOAN 8 HK1 CO DAP AN

4 )

e. 3x

2

– 3xy – 5x + 5y f. 3x

2

+ 6xy + 3y

2

– 3 z

2

= (3x

2

– 3xy ) – (5x - 5y) = 3(x

2

+ 2xy + y

2

– z

2

)

= 3x( x – y) – 5( x – y) = 3[(x

2

+ 2xy + y

2

) – z

2

]

= ( x – y)( 3x – 5) = 3[( x + y )

2

– z

2

]

= 3 ( x + y – z )( x + y + z )

g. 2xy – x

2

– y

2

+ 16 h. 2x – 2y – x

2

+ 2xy – y

2

= 16 – ( x

2

– 2xy + y

2

) = ( 2x – 2y ) – ( x

2

– 2xy +y

2

)

= 4

2

– ( x – y )

2

= 2( x – y ) – ( x – y)

2

= [ 4 – ( x – y )][ 4 + ( x – y )] = ( x – y )[ 2 – ( x – y )]

= ( 4 – x + y )( 4 + x – y ) = ( x – y )( 2 – x + y )