Question

Найдите сумму n первых членов геометрической прогрессии B1=1.q=-1/3.N=4

Answer 1

S4 = b1(q^4-1)/(q - 1) = 1·(-1/3)^4 -1)/(-1/3 -1) = (1/81 - 1) / -4/3 = -80/81 : (-4/3)= =20/27