1: \(=4\left(x^2-\dfrac{3}{2}x+\dfrac{7}{4}\right)\)
\(=4\left(x^2-2\cdot x\cdot\dfrac{3}{4}+\dfrac{9}{16}+\dfrac{19}{16}\right)\)
\(=4\left(x-\dfrac{3}{4}\right)^2+\dfrac{19}{4}>=\dfrac{19}{4}\)
Dấu = xảy ra khi x=3/4
2: \(=9x^2-6x+1+2=\left(3x-1\right)^2+2>=2\)
Dấu = xảy ra khi x=1/3
3: \(=x^2-3x+\dfrac{9}{4}+\dfrac{19}{4}=\left(x-\dfrac{3}{2}\right)^2+\dfrac{19}{4}>=\dfrac{19}{4}\)
Dấu = xảy ra khi x=3/2
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