a: \(=2\left(x^2-5x+\dfrac{3}{2}\right)\)
\(=2\left(x^2-2\cdot x\cdot\dfrac{5}{2}+\dfrac{25}{4}-\dfrac{19}{4}\right)\)
\(=2\left(x-\dfrac{5}{2}\right)^2-\dfrac{19}{2}>=-\dfrac{19}{2}\)
Dấu '=' xảy ra khi x=5/2
b: \(=3\left(x^2-3x-\dfrac{4}{3}\right)\)
\(=3\left(x^2-3x+\dfrac{9}{4}-\dfrac{43}{12}\right)\)
\(=3\left(x-\dfrac{3}{2}\right)^2-\dfrac{43}{4}>=-\dfrac{43}{4}\)
Dấu '=' xảy ra khi x=3/2
c: \(=5\left(x^2-2x-\dfrac{3}{5}\right)\)
\(=5\left(x^2-2x+1-\dfrac{8}{5}\right)\)
\(=5\left(x-1\right)^2-8>=-8\)
Dấu = xảy ra khi x=1
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