4 и 5 задание досконально...........

4. b2=4; b4=1; qgt;0
b4=b1q^3
b2=b1q

b1q^3=1
b1q=4
Разделим 1-ое уравнение на 2-ое:
q^2=1/4
q=1/2

b1=b2:q=4:1/2=8

b1(q^61) 8(-63/64)
S6 = --------------- = --------------- =
q1 1/2

= -63/8:(-1/2) = (632)/8 = 15,75

5. b1=35; b5=7/125
b5=b1q^4
q^4=b5:b1
q^4=7/(12535)
q^4=1/625
q=1/5:
b2=b1q=351/5=7
b3=b1q^2=351/25=7/5
b4=b1q^3=351/125=7/25
b5=b1q^4=351/625=7/125
q=-1/5:
b2=b1q=35(-1/5)=-7
b3=b1q^2=351/25=7/5
b4=b1q^3=35(-1/125)=-7/25
b5=b1q^4=351/625=7/125