toán 9 tìm min

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transformers123

A=8a2+b4a+b2A=\dfrac{8a^2+b}{4a}+b^2

    A==2a+b4a+b2\iff A==2a+\dfrac{b}{4a}+b^2

    A=(a2+b4a+b2)+3a2\iff A=(\dfrac{a}{2}+\dfrac{b}{4a}+b^2)+\dfrac{3a}{2}

    A3a2.b4a.b23+3a2\iff A \ge 3\sqrt[3]{\dfrac{a}{2}.\dfrac{b}{4a}.b^2}+\dfrac{3a}{2}

    A3b2+3a2\iff A \ge \dfrac{3b}{2}+\dfrac{3a}{2}

    A32\iff A \ge \dfrac{3}{2}

Vậy GTNN\mathfrak{GTNN} của A=32A=\dfrac{3}{2} khi x=y=12x=y=\dfrac{1}{2}
 
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