Question

tìm min

a)a=x^2-7x+11

b)a=9x^2+6x+11

 

Answer 1

a: Ta có: \(A=x^2-7x+11\)

\(=x^2-2\cdot x\cdot\dfrac{7}{2}+\dfrac{49}{4}-\dfrac{5}{4}\)

\(=\left(x-\dfrac{7}{2}\right)^2-\dfrac{5}{4}\ge-\dfrac{5}{4}\forall x\)

Dấu '=' xảy ra khi \(x=\dfrac{7}{2}\)

b: ta có: \(A=9x^2+6x+11\)

\(=9x^2+6x+1+10\)

\(=\left(3x+1\right)^2+10\ge10\forall x\)

Dấu '=' xảy ra khi \(x=-\dfrac{1}{3}\)