ĐKXĐ: \(x\ne\pm4\)
Ta có:
\(\dfrac{2x}{x+4}=\dfrac{2x\left(x-4\right)}{\left(x+4\right)\left(x-4\right)}\\ \dfrac{x+3}{4-x}=\dfrac{-\left(x+3\right)}{x-4}=\dfrac{-\left(x+3\right)\left(x+4\right)}{\left(x+4\right)\left(x-4\right)}\)
Vậy: ...
Ta có:
`(2x)/(x + 4) = (2x)/(-(4-x))`
Điều kiện: `-x - 4 \ne0`
`=> x \ne - 4`
`(x+3)/(4-x)`
Điều kiện: `4 - x\ne0`
`=> x\ne4`
Vậy: `x\ne+-4`
\(\dfrac{2x}{x+4}=\dfrac{2x\left(x-4\right)}{\left(x+4\right)\left(x-4\right)}=\dfrac{2x^2-8}{x^2-16}\left(x\ne\pm4\right)\)
\(\dfrac{x+3}{4-x}=\dfrac{-\left(x+3\right)}{x-4}=\dfrac{\left(x+3\right)\left(x+4\right)}{\left(x-4\right)\left(x+4\right)}=\dfrac{-\left(x^2+7x+12\right)}{x^2-16}\left(x\ne\pm4\right)\)
