x2-2x+1=(x-1)2\(\ge0\)
Dấu = xảy ra khi : (x-1)2=0
\(\Rightarrow\)x=1
x2-2x-3=(x2-2x+1)+2=(x-1)2+2\(\ge\)2
Dấu = xảy ra khi : (x-1)2=0
\(\Rightarrow\)x=1
x2-3x+2=(x2-2.1/3x+1/9)+2-1/9=(x-\(\frac{1}{3}\))2+\(\frac{17}{9}\)\(\ge\frac{17}{9}\)
Dấu = xảy ra khi : (x-1/3)2=0
\(\Rightarrow x=\frac{1}{3}\)
2x2+5x-3=2(x2+\(\frac{5}{2}\)x)-3=2(x2+2.\(\frac{5}{4}\)+\(\frac{25}{16}\))-3-2.\(\frac{25}{16}\)=2(x+\(\frac{5}{4}\))2\(-\frac{49}{8}\ge-\frac{49}{8}\)
Dấu = xảy ra khi : 2(x+\(\frac{5}{4}\))2=0
\(\Rightarrow\)x=\(-\frac{5}{4}\)