consider 𝑦=∑∞𝑛=0𝑎𝑛𝑥𝑛 then 𝑦′=∑∞𝑛=1𝑛𝑎𝑛𝑥𝑛−1=∑∞𝑛=0(𝑛+1)𝑎𝑛+1𝑥𝑛 and 𝑦″=∑∞𝑛=2𝑛(𝑛−1)𝑎𝑛𝑥𝑛−2=∑∞𝑛=0(𝑛+2)(𝑛+1)𝑎𝑛+2𝑥𝑛 then solve the equation by normal calculation