`7)`
`(x+2)(x^2-2x+4)-x(x^2+5)=2`
`\to x^3+2^3-x^3-5x=2`
`\to (x^3-x^3)-5x+2^3=2`
`\to -5x+8=2`
`\to -5x=-6`
`\to x=6/5`
Vậy `x=6/5`
`8)`
`(2+x)(x^2-x+1)-x(x^2-2)=19+x^2`
`\to (x^3+x^2-x+2)-(x^3-2x)=19+x^2`
`\to x^3+x^2-x+2-x^3+2x=x^2+19`
`\to (x^3-x^3)+x^2+(2x-x)+2=x^2+19`
`\to x^2+x+2=x^2+19`
`\to x^2-x^2+x=19-2`
`\to x=17`
Vậy `x=17`
`9)`
`(12x-5)(4x-1)+(3x-7)(1-16x)=81`
`\to (48x^2-32x+5)+(-48x^2+115x-7)=81`
`\to 48x^2-32x+5-48x^2+115x-7=81`
`\to (48x^2-48x^2)+(115x-32x)+(5-7)=81`
`\to 83x-2=81`
`\to 83x=83`
`\to x=1`
Vậy `x=1`
