Đáp án:
`a)S={-2}`
`b)S={-2}`
Giải thích các bước giải:
`a)`
`(x+3)^3-x(x-3)(x+3)=-9`
`<=>(x+3)^3-x(x^2-9)=-9`
`<=>x^3+3x^2 .3 +3x.3^2 +3^3 -x^3 +9x=-9`
`<=>x^3+9x^2+27x+27-x^3+9x+9=0`
`<=>9x^2+36x+36=0`
`<=>x^2+4x+4=0`
`<=>(x+2)^2=0`
`<=>x+2=0`
`<=>x=-2`
Vậy `S={-2}`
`b)`
Cách 1:
`(x-1)^3-4x(x^2-1)+3(x^3-1)+3(x^2-2x+1)=5x+7`
`<=>(x-1).(x-1)^2-4x(x-1).(x+1)+3(x-1).(x^2+x+1)+3(x-1)^2=5x+7`
`<=>(x-1).[(x-1)^2-4x(x+1)+3(x^2+x+1)+3(x-1)]=5x+7`
`<=>(x-1).(x^2-2x+1-4x^2-4x+3x^2+3x+3+3x-3)=5x+7`
`<=>(x-1).1=5x+7`
`<=>x-1=5x+7`
`<=>4x=-8`
`<=>x=-2`
Vậy `S={-2}`
______________________
Cách 2:
`(x-1)^3-4x(x^2-1)+3(x^3-1)+3(x^2-2x+1)=5x+7`
`<=>x^3-3x^2 +3x-1-4x^3+4x+3x^3-3+3x^2-6x+3=5x+7`
`<=>(x^3-4x^3+3x^3)+(-3x^2+3x^2)+(3x+4x-6x)+(-1-3+3)=5x+7`
`<=>x-1=5x+7`
`<=>5x-x=-1-7`
`<=>4x=-8`
`<=>x=-2`
Vậy `S={-2}`
