Đáp án+Giải thích các bước giải:
`a)(x-7)(x-5)`
`=x^2-5x-7x+35`
`=x^2-12x+35`
`.............................`
`b)4(x-1)(x+1)`
`=4(x^2-1)`
`=4x^2-4`
`....................`
`c)(\sqrt{x}-1)(\sqrt{x}+5)`
`=x+5\sqrt{x}-\sqrt{x}-5`
`=x+4\sqrt{x}-5`
`................................`
`d)(x^2-2x+1)(x-1)`.
`=(x-1)^2 (x-1)`
`=(x-1)^3`
`=x^3-3x^2+3x-1`
`...............................`
`e)(x+3)(x^2-3x+5)`
`=x^3-3x^2+5x+3x^2-9x+15`
`=x^3-4x+15`
`................................`
`f)(x-2\sqrt{x}+3)(\sqrt{x}-5)`
`=x.\sqrt{x}-2x+3\sqrt{x}-5x+10\sqrt{x}-15`
`=x.\sqrt{x}-12\sqrt{x}-7x-15`
`.................................`
`g)(1/2x-1)(2x-3)`
`=x^2-3/2x-2x+3`
`=x^2-7/2x+3`
`...........................`
`h)(\sqrt{x}-1/2.\sqrt{y})(\sqrt{x}-1/2.\sqrt{y})`
`=(\sqrt{x}-1/2.\sqrt{y})^2`
`=x-\sqrt{x}.\sqrt{y}+y`
`...............................`
`i)(5.\sqrt{x}+2)(5.\sqrt{x}-1)`
`=25x-5.\sqrt{x}+10\sqrt{x}-2`
`=25x+5.\sqrt{x}-2`
`.............................`
`k)(\sqrt{x}+2)(x-2.\sqrt{x}-9)`
`=x.\sqrt{x}-2x-9.\sqrt{x}+2x-4\sqrt{x}-18`
`=x.\sqrt{x}-13.\sqrt{x}-18`
`___________________________`
Chúc bạn học tốt!!!
`#Rùa~ ~ ~`
