[MoO_O~^^]

ข้อ 3
$a^2+b^2=6ab$
$(a+b)^2-2ab=6ab --> (a+b)^2=8ab --> a+b=\sqrt{8ab}$
$(a-b)^2+2ab=6ab --> (a-b)^2=4ab --> a-b=\sqrt{4ab}$
$\frac{a-b}{a+b}=\sqrt{\frac{4ab}{8ab}}=\frac{1}{\sqrt{2}}=\frac{\sqrt{2}}{2}$
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