How do I get sound output from the TV (and not the laptop) when I connect my MacBook Air to a TV usi

How do I get sound output from the TV (and not the laptop) when I connect my MacBook Air to a TV using Mini Display Port to VGA Adapter? When I connect my late 2010 13" MacBook Air using the Mini Display Port to VGA Adapter to my Samsung 19" TV or to ...

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