Question

÷1,7,13,19,......a₁₀=?

Answer 1

$\displaystyle 1,7,13,19~~~~~~~~~~~~~~a_{10}=? \\ a_1=1,~a_2=7,~a_3=13,~a_5=19 \\ r=7-1 \Rightarrow r=6 \\ a_{10}=a_{10-1}+r \Rightarrow a_{10}=a_9+r \Rightarrow a_{10}=a_1+9r \Rightarrow a_{10}=1+9 \cdot 6 \Rightarrow \\ \Rightarrow a_{10}=1+54 \Rightarrow \boxed{a_{10}=55 }$