формулы:[r] [m]\int\frac{du}{u}=ln|u|+C; \int\frac{dx}{x^2+a^2}=\frac{1}{a}arctg\frac{x}{a}+C[/m]; [/r]
[m]a^2=\frac{7}{9}[/m]
[m]=\frac{1}{9\cdot 2}\cdot\int\frac{2x}{x^2+\frac{7}{9}}dx-\frac{1}{9}\cdot 3\cdot \frac{1}{\sqrt{\frac{7}{9}}} arctg \frac{x}{\sqrt{\frac{7}{9}}}+C=[/m]
[m]=\frac{1}{18}\cdot ln |x^2+\frac{7}{9}|-\frac{1}{\sqrt{7}}arctg \frac{3x}{\sqrt{7}}+C[/m]