b1=0,02 bn=312,5 n=7 найти q=? и Sn=?

bn=b1*q^(n-1)q^(n-1)=bn/b1q^(n-1)=312,5/0,02=15625q^(n-1)=5^6n-1=6n=7S7=b1*(q^7-1)/(q-1)S7=0,02(78125-1)/(7-1)=0,02*78124/6=1562,48/6=260 31/75