\[\boxed{\text{290\ (290).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ 6x - 12x + 15x - 9x = 0\]
\[\boxed{\text{290.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ a^{6} \cdot a^{6} = a^{12}\]
\[2)\ a^{4} \cdot a^{8} = a^{12}\]
\[3)\ a^{3} \cdot a^{9} = a^{12}\]
\[4)\ a^{5} \cdot a^{7} = a^{12}\]
\[5)\ a \cdot a^{11} = a^{12}\]