No they can not be used vice versa
you can use LCD TV as PC monitor. but you can't use LCD monitor as TV, as it will not contain TV tuner, and more over the resolution on offer with the monitor makes it unsuitable for long distance viewing i.e., normal TV viewing is not that great on monitors. now a days some monitors are coming with inbuilt TV tuners.
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Posted again:
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No they can not be used vice versa
you can use LCD TV as PC monitor. but you can't use LCD monitor as TV, as it will not contain TV tuner, and more over the resolution on offer with the monitor makes it unsuitable for long distance viewing i.e., normal TV viewing is not that great on monitors. now a days some monitors are coming with inbuilt TV tuners.
and for the difference of price the TV contains Tuner and speakers and it is optimized for TV viewing and monitors are not.