\[2a^{2},\ \ \ 5a^{2},\ \ \ 8a^{2},\ \ \ 11a^{2},\ \ldots;\]
\[d = 5a^{2} - 2a^{2} = 3a^{2};\]
\[c_{n} = 2a^{2} + 3a^{2}(n - 1) =\]
\[= 2a^{2} + 3a^{2}n - 3a^{2}\]