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Miley Cyrus is, no doubt, a hard-working pop star ... and to get some much-needed R&R, the former Hannah Montana star has left the country!

The Can't Be Tamed singer, and her gorgeous mom Tish, are spending time on the beach in Brazil. Now THAT'S a vacation.

We can't help but notice Miley's tousled hair. Guess she can blame it on Rio! See the 18-year-old bikini bod (from the back) ... after the jump.