`17) 1/((x-1)(x^2+x+1)) = (x+1)/(x^2+x+1)(Đk:xne1)`
`<=> 1/((x-1)(x^2+x+1)) = ((x+1)(x-1))/((x-1)(x^2+x+1)`
`<=> 1 = (x+1)(x-1)`
`<=> 1 = x^2-1`
`<=> x^2-1-1=0`
`<=> x^2=2`
`<=> x=+-sqrt2`
`18)( 2x-1)/(x^3+1) + 2/(x+1) = 2x/(x^2-x+1)(Đk:xne-1)`
`<=>( 2x-1)/((x+1)(x^2-x+1)) + (2(x^2-x+1))/((x+1)(x^2-x+1)) = (2x(x+1))/((x+1)(x^2-x+1)`
`<=> 2x-1 + 2(x^2-x+1) = 2x(x+1)`
`<=> 2x-1 + 2(x^2-x+1) - 2x(x+1)=0`
`<=> 2x-1 + 2x^2-2x+2 - 2x^2-2x=0`
`<=> -2x+1 =0`
`<=>x=1/2`
