Verified answer

а)b1=1 b2=1/3
q=b2/b1=>q=(1/3)/1;=>q=1/3
S=b1/(1-q);
S=1/(1-1/3);=>S=1/(2/3)=3/2=1,5;

б)b1=3 b2=1/3
q=(1/3)/3=1/9;
S=3/(1-1/9)=3/(8/9)=27/8=3 и 3/8

в)b1=1 b2=3/4
q=(3/4)/1=3/4;
S=1/(1-3/4)=1/(1/4)=4;

Ответ:а)1,5;б)3 и 3/8;в)4