Упростите выражение: (a+3c)^2+(b+3c)(b-3c).

\[(a + 3c)^{2} + (b + 3c)(b - 3c) =\]

\[= a^{2} + 6ac + 9c^{2} + b^{2} - (3c)^{2} =\]

\[= a^{2} + 6ac + 9c^{2} + b^{2} - 9c^{2} =\]

\[= a^{2} + 6ac + b^{2}\text{.\ }\]