Respostas

2014-02-18T15:05:56-03:00
Para x  Natural e menor que 21, temos 21 números {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}