The line should be
7 a 2 = a 0 − 2 a 1 = ( 1 + 4 5 ) a 0 , ⟹ a 2 = 9 35 a 0 , {\displaystyle 7a_{2}=a_{0}-2a_{1}=\left(1+{\frac {4}{5}}\right)a_{0},\quad \Longrightarrow \quad a_{2}={\frac {9}{35}}a_{0},}
Return to errata.
