Question

найдите сумму первых 5 членов геометрической прогрессии:54;36;...;

Answer 1

q = 36/54 = 2/3
сумма  S(5) = b1(q^n-1) / (q-1) = 54*((2/3)^5-1)/(2/3-1)= 422/3

Answer 2

q=b2/b1
q = 36/54 = 2*18/3*18=2/3
S(5) = b1(q^n-1)/(q-1) = 54*((2/3)^5-1)/(2/3-1)= 54(32/243-1)/-1/3=422/3