10.
$ x + \frac{2+\sqrt{2}}{2-\sqrt{2}} = 10 - y\sqrt{2}$
$ x + \frac{(2+\sqrt{2})(2+\sqrt{2})}{(2-\sqrt{2})(2+\sqrt{2})} = 10 - y\sqrt{2}$
$ x + \frac{4 + 4\sqrt{2} +2}{2} = 10 - y\sqrt{2}$
$ (x + 3) + 2\sqrt{2} = 10 - y\sqrt{2}$
เทียบสัมประสิทธิ์
จะได้ $x = 7$ และ $y =-2$
$\therefore x - y = 7 - (-2) = 9$
#กล้วยๆ
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