Question

Найдите сумму семи членов геометрической прогрессии -2,-4,-8

Answer 1

-2; -4; -8;...
q = -4:(-2) = 2
S₇ = b₁(q⁷-1)/(q -1)
S₇ = -2*(2⁷-1)/(2 -1) = -2*127 = -254