Đáp án + Giải thích các bước giải :
`27x^3-54x^2+36x=9`
`<=>27x^3-54x^2+36x-9=0`
`<=>[(3x)^3-3*(3x)^2*2+3*3x*2^2-2^3]-1=0`
`<=>(3x-2)^3=1`
`<=>3x-2=1`
`<=>3x=3`
`<=>x=1`
Vậy `S={1}`.
Đáp án:
`27x³-54x²+36x=9`
`⇔9x(3x²-6x+4)=9`
`⇔x(3x²-6x+4)=1`
TH1: `x=1`
`⇒ 3x²-6x+4=1`
`⇔3x²-6x+3=0`
`⇔3(x²-2x+1)=0`
`⇔(x-1)²=0⇔x=1`
TH2: `x=-1`
`⇒ 3x²-6x+4=-1`
`⇔3x²-6x+5=0`
`⇔3(x²-2x+5)=0`
`⇔3[(x²-2x+4)+1]=0`
`⇔3[(x+1)²+1]=0`
`⇔(x+1)²+1=0` (vô nghiệm)
Vậy: `x=1`
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