4. b2=4; b4=1; q>0
b4=b1•q^3
b2=b1•q
b1•q^3=1
b1•q=4
Разделим первое уравнение на второе:
q^2=1/4
q=1/2
b1=b2:q=4:1/2=8
b1•(q^6–1) 8•(-63/64)
S6 = --------------- = --------------- =
q–1 –1/2
= -63/8:(-1/2) = (63•2)/8 = 15,75
5. b1=35; b5=7/125
b5=b1•q^4
q^4=b5:b1
q^4=7/(125•35)
q^4=1/625
q=1/5:
b2=b1•q=35•1/5=7
b3=b1•q^2=35•1/25=7/5
b4=b1•q^3=35•1/125=7/25
b5=b1•q^4=35•1/625=7/125
q=-1/5:
b2=b1•q=35•(-1/5)=-7
b3=b1•q^2=35•1/25=7/5
b4=b1•q^3=35•(-1/125)=-7/25
b5=b1•q^4=35•1/625=7/125