câu 49: Rút gọn các biểu thức sau
1) x ( x – 2 ) – 5 ( x – 1 ) ( x + 9 )
2) ( 4x + 3 ) ( 2 – y ) + ( y + 1 ) ( x – 5 )
3) ( x + 5 ) ( x -1 ) + ( 2x – 3 ) ( x -7 ) – 3 ( x – 1 ) ( x + 1 )
câu 49: Rút gọn các biểu thức sau
1) x ( x – 2 ) – 5 ( x – 1 ) ( x + 9 )
2) ( 4x + 3 ) ( 2 – y ) + ( y + 1 ) ( x – 5 )
3) ( x + 5 ) ( x -1 ) + ( 2x – 3 ) ( x -7 ) – 3 ( x – 1 ) ( x + 1 )
`x(x-2)-5(x-1)(x+9)`
`= x^2 – 2x – 5(x-1)(x+9)`
`= x^2 – 2x – 5x^2 – 40x + 45`
`= -4x^2- 42x+45`
`(4x+3)(2-y)+(y+1)(x-5)`
`= 8x – 4xy + 6 – 3y + (y+1)(x-5)`
`= 8x – 4xy + 6 -3y+xy-5y+x-5`
`= 9x – 3xy + 1 – 8y`
`(x+5)(x-1) + (2x-3)(x-7) – 3(x-1)(x+1)`
`= x^2 + 4x- 5+(2x-3)(x-7)-3(x-1)(x+1)`
`= x^2 + 4x – 5 + 2x^2 – 17x + 21-3(x-1)(x+1)`
`= x^2 + 4x – 5 + 2x^2 – 17x + 21 – 3x^2 + 3`
`= -13x + 19`
`1)x(x-2)-5(x-1)(x+9)`
`=x^2-2x-5x^2-40x+45`
`=-4x^2-42x+45`
`2)(4x+3)(2-y)+(y+1)(x-5)`
`=8x-4xy+6-3y+xy-5y+x-5`
`=9x-3xy+1-8y`
`3)(x+5)(x-1)+(2x-3)(x-7)-3(x-1)(x+1)`
`=x^2-x+5x-5+2x^2-14x-3x+21-3(x^2-1)`
`=x^2+4x-5+2x^2-17x+21-3x^2+3`
`=-13x+19.`