1. bn+1=4bn + 7; b1=–3
b2=4•(–3)+7=–5
b3=4•(–5)+7=–13
b4=4•(–13)+7=–45
2. b1=9; q=1/3
b6=b1•q^5=9•1/243=1/27
b1•(q^6–1) 9•(–728/729)
S6 = --------------- = ------------------- =
q–1 –2/3
728•3 364 13
= ---------- = ------- = 13 -----
81•2 27 27
3. а3=а1+2d
a8=a1+7d
a1+7d=25
a1+2d=0
5d=25
d=5
a1=a3–2d=0–2•5=–10
a6=a1+5d=–10+5•5=15
4. b2•b8=36
b1•q•b1•q^7=36
b1^2•q^8=36
Извлекаем из корня обе части уравнения:
b1•q^4=6
b5=b1•q^4=6