a) \(x=3k-2\) ta có:
\(\Rightarrow A = \left\{-2; \, 1; \, 4; \, 7; \, 10; \, 13\right\}\)
b) \(B =\)\( \left\{0; \, 1; \, 2; \, 3; \,4; \, 5; \, 6; \, 7; \, 8; \, 9; \, 10; \, 11; \, 12\right\}\)
c) \(x=(-1)^n\)
+) Với \(n=2k \, \, (k \in N)\) ta có: \(x=(-1)^{2k}=1.\)
+) Với \(n=2k+1 \, \, (k \in N)\) ta có: \(x=(-1)^{2k+1}=(-1)^{2k}. (-1)^1=-1.\)
\(\Rightarrow C = {\rm{\{ }}1; - 1\} .\)