3) `(3x-1)(2x+7)-(x+1)(6x-5)=16`
⇔`6x^2+21x-2x-7-6x^2+5x-6x+5=16`
⇔`18x=16-5+7`
⇔`18x=18`
⇔`x=1`
Vậy `S={1}`
4) `(3x+1)(-x+2)+(2-x)(1-3x)=7-5x`
⇔`-3x^2+6x-x+2+2-6x-x+3x^2+5x-7=0`
⇔`3x=7-2-2`
⇔`3x=3`
⇔`x=1`
Vậy `S={1}`
5) `x^3+3x^2+3x+1=0`
⇔`(x+1)^3=0`
⇔`x+1=0`
⇔`x=-1`
Vậy `S={-1}`
6) `(2x+1)(4x^2-2x+1)-8x(x^2+2)=17`
⇔`8x^3+1-8x^3-16x=17`
⇔`-16x=17-1`
⇔`-16x=16`
⇔`x=-1`
Vậy `S={-1}`