Question

Найти суму первых 5 членов геометрической прогресии если b5=112,q=2

Answer 1

b5 = b1*q^4 = b1*2^4 = b1*16 = 112
b1 = 112/16 = 7
S(5) = b1*(q^5 - 1)/(q - 1) = 7*(2^5 - 1)/(2 - 1) = 7*31 = 217