a: \(=x^2-4x+4-2=\left(x-2\right)^2-2>=-2\)
Dấu '=' xảy ra khi x=2
b: \(=x^2+x+\dfrac{1}{4}+\dfrac{7}{4}=\left(x+\dfrac{1}{2}\right)^2+\dfrac{7}{4}>=\dfrac{7}{4}\)
Dấu '=' xảy ra khi x=-1/2
c: \(=x^2-x+\dfrac{1}{4}+\dfrac{11}{4}=\left(x-\dfrac{1}{2}\right)^2+\dfrac{11}{4}>=\dfrac{11}{4}\)
Dấu '=' xảy ra khi x=1/2
d: \(=x^2-6x+9-4=\left(x-3\right)^2-4>=-4\)
Dấu '=' xảy ra khi x=3