G = x2 - x + 10
= \(\left[x^2-2.x.\dfrac{1}{2}+\left(\dfrac{1}{2}\right)^2\right]+\dfrac{39}{4}\)
= \(\left(x-\dfrac{1}{2}\right)^2+\dfrac{39}{4}\)
Ta thấy: \(\left(x-\dfrac{1}{2}\right)^2\ge0\forall x\in R\)
=> \(\left(x-\dfrac{1}{2}\right)^2+\dfrac{39}{4}\ge\dfrac{39}{4}\)
=> Min G = \(\dfrac{39}{4}\)\(\Leftrightarrow\left(x-\dfrac{1}{2}\right)^2=0\)
\(\Leftrightarrow x=\dfrac{1}{2}\)
Vậy Min G = 39/4 khi x = 1/2
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