Question

Determine a razão da P.A. onde a1=$\frac{1}{5}$ e a9=$\frac{17}{5}$.

Answer 1

$an=a1+(n-1).r \\ \\ a9=a1+(9-1).r \\ \\ a9=a1+8r \\ \\ \frac{17}{5}= \frac{1}{5}+8r \\ \\ 17=1+40r \\ \\ 16=40r \\ \\ r= \frac{16}{40} \\ \\ r= \frac{2}{5}$