Question

Answer 1

Bài 4: 

a: \(x^2+x+1\)

\(=x^2+2\cdot x\cdot\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{3}{4}\)

\(=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4}\forall x\)

Dấu '=' xảy ra khi \(x=-\dfrac{1}{2}\)

c: \(x^2-4x+1\)

\(=x^2-2\cdot x\cdot2+4-3\)

\(=\left(x-2\right)^2-3\ge-3\forall x\)

Dấu '=' xảy ra khi x=2