Đáp án:
`a)S={25/18}`
`b)S={1}`
`c)S={27}`
Giải thích các bước giải:
`a)(4x+1)(x-3)=(x-7)(4x-1)+15`
`⇔4x²-12x+x-3=4x²-x-28x+7+15`
`⇔4x²-11x-3=4x²-29x+22`
`⇔4x²-11x-4x²+29x=22+3`
`⇔18x=25`
`⇔x=25/18`
Vậy `S={25/18}`
`b)(x+1)(x²-x+1)-x(x²-3)=4`
`⇔x³+1-x³+3x=4`
`⇔3x+1=4`
`⇔3x=4-1`
`⇔3x=3`
`⇔x=3:3`
`⇔x=1`
Vậy `S={1}`
`c)(x-3)(x²+3x+9)+x(5-x²)=6x`
`⇔(x-3)[x²+x.3+3²]+5x-x³=6x`
`⇔x³-3³+5x-x³=6x`
`⇔5x-27=6x`
`⇔5x-6x=27`
`⇔-x=27`
`⇔x=-27`
Vậy `S={-27}`