Question

Answer 1

`F=[x^2-4x+5]/[x^2-4x+6]=1-1/[x^2-4x+6]=1-1/[(x-2)^2+2]`

Vì `(x-2)^2 >= 0 AA x<=>(x-2)^2+2 >= 2 AA x`

        `=>1/[(x-2)^2+2] <= 1/2 AA x`

        `=>-1/[(x-2)^2+2] >= -1/2 AA x<=>F >= 1/2 AA x`

Dấu "`=`" xảy ra `<=>x-2=0<=>x=2`

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`D=[x^2-4x+10]/[x^2-4x+6]=1+4/[x^2-4x+6]=1+4/[(x-2)^2+2]`

Vì `(x-2)^2 >= 0 AA x<=>(x-2)^2+2 >= 2 AA x`

           `<=>4/[(x-2)^2+2] <= 2 AA x<=>D <= 3 AA x`

Dấu "`=`" xảy ra `<=>x-2=0<=>x=2`