`a, (x² – 2x + 3) (1/2x – 5)`
`=1/2x³ – 5x² – x² +10x + 3/2x – 15`
`= 1/2x³ – 6x² + 23/2x -15`
`b) (x² – 2xy + y²)(x – y)`
`= (x² – 2xy + y²).x + (x² – 2xy + y²).(–y)`
`= x².x + (–2xy).x + y².x + x².(–y) + (–2xy).(–y) + y².(–y)`
`= x³ – 2x²y + xy² – x²y + 2xy² – y³`
`= x³ – (2x²y + x²y) + (xy² + 2xy²) – y²`
`= x³ – 3x²y + 3xy² – y³`
Xin hay nhất !