Hej!
1]
[tex]a_n=\frac{1+(-1)^n}{n}\\\\a_1=\frac{1+(-1)^1}{1}=\frac{1+(-1)}{1}=\frac{0}{1}=\boxed0\\\\a_2=\frac{1+(-1)^2}{2}=\frac{1+1}{2}=\frac{2}{2}=\boxed1\\\\a_3=\frac{1+(-1)^3}{3}=\frac{1+(-1)}{3}=\frac{0}{3}=\boxed0\\\\a_4=\frac{1+(-1)^4}{4}=\frac{1+1}{4}=\frac{2}{4}=\boxed{0,5}\\\\a_5=\frac{1+(-1)^5}{5}=\frac{1+(-1)}{5}=\frac{0}{5}=\boxed0[/tex]
2]
[tex]a_1=4, \ a_3=10\\\\a_3=a_1+2r\\\\4+2r=10\rightarrow r=3\\\\----------\\\\a_1=\boxed4\\\\a_2=a_1+r=4+3=\boxed7\\\\a_3=\boxed{10}\\\\a_4=a_3+r=10+3=\boxed{13}\\\\a_5=a_4+r=13+3=\boxed{16}[/tex]
