`a)[x\sqrt{x}+y\sqrt{y}]/[\sqrt{x}+\sqrt{y}]-\sqrt{xy}`
`=[(\sqrt{x}+\sqrt{y})(x-\sqrt{xy}+y)]/[\sqrt{x}+\sqrt{y}]-\sqrt{xy}`
`=x-\sqrt{xy}+y-\sqrt{xy}=(\sqrt{x}-\sqrt{y})^2`
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`b)[a+\sqrt{ab}]/[b+\sqrt{ab}]`
`=[\sqrt{a}(\sqrt{a}+\sqrt{b})]/[\sqrt{b}(\sqrt{a}+\sqrt{b})]`
`=[\sqrt{a}]/\sqrt{b}`
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`c` đề bị che mất mẫu
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