a) P=$\sqrt[]{x^2-2x+5}$
`=`$\sqrt[]{x^2-2x+1+4}$
`=`$\sqrt[]{(x-1)^2+4}$`>=`$\sqrt[]{4}$`=2`
Dấu = có khi `x-1=0<=> x=1`
Vậy `min P=2` khi `x=1`
`b) Q=5-`$\sqrt[]{x^2-4x+7}$
`=5-`$\sqrt[]{x^2-4x+4+3}$
`=5-`$\sqrt[]{(x-2)^2+3}$`<=5-`$\sqrt[]{3}$
Dấu = có khi `x-2=0<=> x=2`
Vậy `max Q=5-`$\sqrt[]{3}$ khi `x=2`