Giải nhanh giúp em bài này với ạaaa!

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Giải nhanh giúp em bài này với ạaaa!

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    `a)`

    `\sqrt{x^2 -4x+7)=\sqrt{x+1}`

    `<=> {(x>= -1),(x^2 -4x+7=x+1):}`

    `<=> {(x>= -1),(x^2 -5x+6=0):}`

    `<=> [(x=2),(x=3):}`.

    `b)`

    ` {(1/(x-y) + 1/(x+y) =2),(2/(x+y) + 3/(x+y)=5):} (1) (ĐKXĐ: x \ne +-y)`

    Đặt ` {(u=1/(x+y)),(v=1/(x-y)):}`

    `(1) <=> {(u+v=2),(2u+3v=5):}`

    `<=> {(3u+3v=6),(2u+3v=5):}`

    `<=> {(u=1),(v=1):}`

    `=> {(1/(x+y)=1),(1/(x-y) =1):}`

    `<=> {(x+y=1),(x-y=1):}`

    `<=> {(x=1),(y=0):}`.

     

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