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La R (chiamata erre in italiano) è la sedicesima lettera dell'alfabeto italiano.
tale simbolo è poi usato in vari modi nell'alfabeto fonetico internazionale: [r] indica una consonante vibrante alveolare, [R] una vibrante uvulare.
take a look here and you'll see how many few countries have these sounds for R.
http://en.wikipedia.org/wiki/R
Listen to these ones:
http://upload.wikimedia.org/wikipedia/commons/c/ce/Alveolar_trill.ogg
http://upload.wikimedia.org/wikipedia/commons/6/60/Alveolar_flap.ogg
Many persons not only from your country don't have these sounds in their alphabet that's why it seem difficult to you to pronunciate, but you'd better see with your eyes what to do these sounds and then do if yourself :)
La back part of the toungue in low, while the front part and the tip are raised; the tip stays behind upper teeth, without touch 'm and without touching the palate, it's hanging. The soudn that exit is guttural, and the toungue vibrates, without to touch the walls of the mouth.
Lips , outside, from half-closed open lightly when the sound comes out of the mouth (lower lip go down) then half close again.
It's very difficult to do it without seeing each other in person... i know.. but try!