[tex]\displaystyle\bf\\\boxed{a_{n} =a_{1} +d\cdot(n-1)}\\\\\\1)\\\\a_{1} =11 \ \ \ ; \ \ \ d=\frac{1}{2} \\\\a_{11} =a_{1} +10d=11+10\cdot \frac{1}{2} =11+5=16\\\\2)\\\\a_{1} =-3 \ \ \ ; \ \ \ d=-4 \\\\a_{11} =a_{1} +10d=-3+10\cdot (-4) =-3-40=-43[/tex]