Answer:
a^4+3a^2-3b^2
Step-by-step explanation:
[tex] \hookrightarrow \: (2 {a}^{2} - b)(3 {a}^{2} + 3b) \\ \hookrightarrow \:2 {a}^{2} (3 {a}^{2} + 3b) - b(3 {a}^{2} + 3b) \\ \hookrightarrow \:6 {a}^{4} + 6 {a}^{2} b - 3 {a}^{2} b - 3 {b}^{2} \\ \hookrightarrow \:{a}^{4} + 3 {a}^{2} b- 3 {b}^{2}[/tex]
