1, `5x3 – 15x2 + 10xy`
`= 5x. (x2 – 3x + 2y)`
2, `x2 + 2x + 1 – 25y2`
`= (x2 + 2x + 1) – 25y2` HĐTsố 1) (A + B)2 = A2 + 2AB + B2
`= (x + 1)2 – (5y)^2`
`= (x + 1 + 5y). (x + 1 – 5y)`
3, `xy – 2x. (x+3) + 3y`
`= (xy + 3y) – 2x. (x + 3)`
`= y. (x + 3) – 2x. (x + 3)`
`= (y – 2x). (x + 3)`
4, `x3 – x2 - x + 1`
`= (x3 – x2) + (-x + 1)`
`= x2. (x – 1) – (x – 1)`
`= (x2 – 1). (x – 1)`
`= (x - 1). (x + 1) . (x – 1)`
`= (x – 1)2. (x + 1)`
5, `2x2 – x + 6xy – 3y`
`= (2x2 – x) + (6xy – 3y)`
`= x. (2x – 1) + 3y. (2x – 1)`
`= (x + 3y). (2x – 1)`
6,` x2 – 8x + 15`
`= x2 – 2.x.4 + 42 + 15 – 4^2`
`= (x – 4)2 – 1`
`= (x – 4)2 – 1^2`
`= (x – 4 + 1). (x – 4 – 1)`
`= (x – 3). (x – 5)`
7, `7x2 – 42x + 63`
`= 7. (x2 – 6x + 9)`
`= 7. (x2 – 2.x.3 + 32)`
`= 7. (x – 3)^2`
8, `x2 – xy – 5x + 5y`
`= (x2 – xy) + (-5x + 5y)`
`= x. (x – y) + 5. (-x + y)`
`= x. (x – y) – 5. (x – y)`
`= (x – 5). (x – y) `
9, `5x. (x – 3)+ 6 – 2x`
= `5x2 – 15x + 6 – 2x`
= `5x2 – 17x + 6`
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