Consider the ring "\\Bbb Z_7[x]" of polynomials in one variable 𝑥 with coefficients in ℤ"_7" It is an infinite ring since "x^m \\in \\Bbb Z_7[x]:=\\{a_1x^m+a_2x^{m-1}+...+a_n:a_1\\ne 0,a_1,...,a_n\\in \\Bbb Z_7\\& m\\in \\Bbb Z^+\\}" and note that for all positive integers 𝑚, and "x^{m_1} \\ne x^{m_2}" for "m_1\\ne m_2" ,Thus "Cardinality( \\Bbb Z_7[x])=\\infty" But the charactetistic of "\\Bbb Z_7[x]" is 7 as 7 is prime and 1+1+1+1+1+1+1=7=0. in the ring "\\Bbb Z_7" .
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