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Với ạaaaaa:)))

`#Zkj `

`3B. `

`a)25x^2+10x+1=0 `

`<=>25x^2+5x+5x+1=0 `

`<=>5x(5x+1)+(5x+1)=0 `

`<=>(5x+1)(5x+1)=0 `

`<=>(5x+1)^2=0 `

`<=>5x+1=0 `

`<=>5x=-1 `

`<=>x=-1/5 `

`=> ` Vậy `S={-1/5} `

`b)x^2-20x=-100 `

`<=>x^2-20x+100=0 `

`<=>(x-10)^2=0 `

`<=>x-10=0 `

`<=>x=10 `

`=> ` Vậy `S={10} `

`c)8x^3-12x^2+6x-1=0 `

`<=>(2x-1)^3=0 `

`<=>2x-1=0 `

`<=>2x=1`

`<=>x=1/2 `

`=> ` Vậy `x=1/2 `

`d)(3x-1)^3+(3x+1)^3=0 `

`<=>27x^3-27x^2+9x-1+27x^3+27x^2+9x+1=0 `

`<=>54x^3+18x=0 `

`<=>18x(3x^2+1)=0 `

`TH1:18x=0 `

`<=>x=0 `

`TH2:3x^2+1=0 `

`<=>3x^2=-1 `

`<=>x^2=-1/3(vô  lí) `

`=> ` Vậy `S={0} `

`4A. `

`a)32^2+64.68+68^2 `

`=32^2+2.32.68+68^2 `

`=(32+68)^2 `

`=100^2 `

`=10000 `

`b)96^2-96.92+46^2 `

`=96^2-96.2.46+46^2 `

`=(96-46)^2 `

`=50^2 `

`=2500 `

`c)221^2-112^2 `

`=(221-112).(221+112) `

`=100.342 `

`=34200 `

`d)11^3+27.11^2+33.9^2+9^3 `

`=11^3+3.9.11^2+3.9^3  .  9^2+9^3 `

`=(11+9)^3 `

`=20^3 `

`=8000 `