`Q = a^2 +b^2 +a - 2b + 1/a + 1/b + 1/(a+b)`

    `= (a^2 +1) + (b^2-4b+4) + a + 2b +1/a + 1/b + 1/(a+b) -5`

`>= 2a + 0 + a + 2b +1/a + 1/b + 1/(a+b) -5 `

`  = 17/9a + 59/36b + a + 1/a + b/4 + 1/b + (a+b)/9 + 1/(a+b) -5`

`>= 17/9 + 59/18 + 2 + 1 + 2/3 - 5`

`= 23/6`

Dấu `''=''` sảy ra khi `a=1 ; b=2`

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