Tìm `x:` `(-x+8)/(x^2 + x+4) = (x^2 -x+4)/(x+8)`
1 câu trả lời
`(-x+8)/(x^2 +x+4) +1 = (x^2 -x+4)/(x+8) + 1`
`=> (-x+8)/(x^2 +x+4) + (x^2 +x+4)/(x^2 +x+4) = (x^2 -x+4)/(x+8) + (x+8)/(x+8)`
`=> (-x+8+x^2 + x+4)/(x^2 +x+4) = (x^2 -x+4+x+8)/(x+8)`
`=> (-x+x+x^2 + 8+4)/(x^2 +x+4)=(-x+x+x^2 +4+8)/(x+8)`
`=> (x^2 +12)/(x^2 +x+4) = (x^2 +12)/(x+8)`
Vì `(x^2 + 12)` $\neq$ `0` $\forall$ `x in QQ` nên:
`x^2 +x+4=x+8`
`=> x^2 +x-x=8-4`
`=> x^2 = 4`
`=> x= +-`$\sqrt{4}$
`=> x= +-2`
Vậy `x in {2; -2}`
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