`***` Lời giải chi tiết `***`
`5)`
`(4x-5)(x+2)-(x+5)(x-3)-3x^{2}-x`
`=4x^{2}-5x+8x-10-(x^{2}+5x-3x-15)-3x^{2}-x`
`=4x^{2}+3x-10-(x^{2}+2x-15)-3x^{2}-x`
`=4x^{2}+3x-10-x^{2}-2x+15-3x^{2}-x`
`=(4x^{2}-x^{2}-3x^{2})+(3x-2x-x)+(15-10)`
`=5`
`=>` đpcm
`6)`
`(x-3)(x+7)-(2x-1)(x+2)+x(x-1)`
`=x^{2}-3x+7x-21-(2x^{2}-x+4x-2)+x^{2}-x`
`=x^{2}+4x-21-(2x^{2}+3x-2)+x^{2}-x`
`=x^{2}+4x-21-2x^{2}-3x+2+x^{2}-x`
`=(x^{2}-2x^{2}+x^{2})+(4x-3x-x)+(2-21)`
`=-19`
`=>` đpcm
`7)`
`(7x-3)(2x+1)-(5x-2)(x+4)-9x^{2}+17x`
`=14x^{2}-6x+7x-3-(5x^{2}-2x+20x-8)-9x^{2}+17x`
`=14x^{2}+x-3-(5x^{2}+18x-8)-9x^{2}+17x`
`=14x^{2}+x-3-5x^{2}-18x+8-9x^{2}+17x`
`=(14x^{2}-5x^{2}-9x^{2})+(x-18x+17x)+(-3+8)`
`=5`
`=>` đpcm
