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Trả lời:
$(5+4\sqrt{2})(3+2\sqrt{1+\sqrt{2}})(3-2\sqrt{1+\sqrt{2}})$
$=(5+4\sqrt{2}).[3^2-(2\sqrt{1+\sqrt{2}})^2]$
$=(5+4\sqrt{2}).[9-4(1+\sqrt{2})]$
$=(5+4\sqrt{2}).(9-4-4\sqrt{2})$
$=(5+4\sqrt{2}).(5-4\sqrt{2})$
$=5^2-(4\sqrt{2})^2$
$=25-16.2$
$=-7$.