Ответ:
\[9a^2+6ab+b^2=(3a+b)^2.\]
\[\sqrt{(3a+b)^2}=|3a+b|=\left|\frac{15}{13}+\frac6{13}\right|=\frac{21}{13}.\]
Ответ: \(\frac{21}{13}\).
\[9a^2+6ab+b^2=(3a+b)^2.\]
\[\sqrt{(3a+b)^2}=|3a+b|=\left|\frac{15}{13}+\frac6{13}\right|=\frac{21}{13}.\]
Ответ: \(\frac{21}{13}\).