[tex]x^{2}-x+1[/tex]
[tex]<=>x^{2}-x+\frac{1}{4}-\frac{1}{4}+1[/tex]
[tex]<=>(x-\frac{1}{2})^{2}+\frac{3}{4}[/tex]
Ta có:[tex](x-\frac{1}{2})^{2}\geq 0[/tex] với mọi x
[tex]=>(x-\frac{1}{2})^{2}+\frac{3}{4}\geq \frac{3}{4}[/tex] với mọi x
Dấu "=" xảy ra [tex]<=>x-\frac{1}{2}=0[/tex]
[tex]<=>x=\frac{1}{2}[/tex]
KL:Min [tex]=\frac{3}{4}[/tex] khi [tex]x=\frac{1}{2}[/tex]