Question

na p a em que a9 =50 e r =2 calcule a1 e a18

Answer 1

$a_n=a_1+(n-1).r\\ a_9=a_1+(9-1).2\\ a_9=a_1+8.2\\ a_9=a_1+16\\ 50=a_1+16\\ a_1=50-16\\ a_1=34\\\\ a_{18}=a_1+(18-1).2\\ a_{18}=34+17.2\\ a_{18}=34+34\\ a_{18}=68$