Question

В геометрической прогрессии bn b3 = 12, b6 = 96. Найти S7

Answer 1

B3=12,b6=96, q=?, s7=?
b6=b3.q³, q³=b6/b3=96/12=8
q=∛8=2, b3=b1q²,b1=12/2²=12/4=3,b1=3
s7=b1.(qˇ7-1)/(q-1)
s7=3.(2ˇ7-1)/(2-1)=3(128-1)/1=3.127=381
Otvet: s7=381