[tex]\displaystyle\bf\\a_{8} +a_{10} =12\\\\1)\\\\a_{9} =\frac{a_{8}+ a_{10} }{2} =\frac{12}{2} =6\\\\Otvet \ : \ a_{9} =6\\\\\\2)\\\\a_{8} +a_{10} =12\\\\a_{1} +7d+a_{1} +9d=12\\\\\boxed{2a_{1} +16d=12}\\\\\\a_{5} +a_{13} =a_{1} +4d+a_{1} +12d=\underbrace{2a_{1} +16d}_{12}=12\\\\Otvet: \ a_{5} +a_{13} =12[/tex]