A) b7=72,9
q=1,5
b(n) =b1*q^(n-1)
S(n) =(b1-b(n)*q)/(1-q)
b1=72,9/1,5^6
=72,9/11,39=6,4
S7=(6,4-72,9*1,5)/(1-1,5)=-102, 95/-0,5=205,9
b) b5=16/9 q=2/3
b1=(16/9):(2/3)^4=(16/9):(16/81)=81/9=9
b7=b1*q^6=9*(2/3)^6=9*(64/729)=64/81
S7=(9-(64/81)*(2/3))/(1-2/3)= (9-128/243)/(1/3)=(2059/243)/(1/3)=6177/243= 25 и102/243= 25 и 34/81
В)
b3=64
q=1/2
b1=64:(1/2)^2=64*4=256
b7=256*(1/2)^6=256/64=4
S7=(256-4*(1/2))/(1-1/2)=254*2=508
Г)b4=81
q=-1/3
b1=81:(-1/3)^3=—81×27=(-2187)
b7=(-2187)*(-1/3)^6=2187/279=3
S7=(-2187-3*(-1/3))/(1+1/3)=-2186/(4/3)=(-1639,5)
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Answers & Comments
A) b7=72,9
q=1,5
b(n) =b1*q^(n-1)
S(n) =(b1-b(n)*q)/(1-q)
b1=72,9/1,5^6
=72,9/11,39=6,4
S7=(6,4-72,9*1,5)/(1-1,5)=-102, 95/-0,5=205,9
b) b5=16/9 q=2/3
b1=(16/9):(2/3)^4=(16/9):(16/81)=81/9=9
b7=b1*q^6=9*(2/3)^6=9*(64/729)=64/81
S7=(9-(64/81)*(2/3))/(1-2/3)= (9-128/243)/(1/3)=(2059/243)/(1/3)=6177/243= 25 и102/243= 25 и 34/81
В)
b3=64
q=1/2
b1=64:(1/2)^2=64*4=256
b7=256*(1/2)^6=256/64=4
S7=(256-4*(1/2))/(1-1/2)=254*2=508
Г)b4=81
q=-1/3
b1=81:(-1/3)^3=—81×27=(-2187)
b7=(-2187)*(-1/3)^6=2187/279=3
S7=(-2187-3*(-1/3))/(1+1/3)=-2186/(4/3)=(-1639,5)