665. б) S5=b1*(q^4–1)/(q–1)=(4*80)/(-4)=–80
г) S5=b1*(q^4–1)/(q–1)=(-1/3*15)/(-3)=
=5/3
д) b3=b1*q^2
q^2=b3/b1=2
q=/2 (корень из 2)
S5=b1*(q^4–1)/(q–1)=(1*3)/(/2–1)=
=3:(/2–1)
666. S6=b1*(q^5–1)/(q–1)=
=48*(-33/32):(-3/2)=
=(48*(-33)*2)/(32*(-3))=528/16=33
667. S100=b1*(q^99–1)/(q–1)=
=(1*(-2)/(-2)=1
S101=b1*(q^100–1)/(q–1)=
=(1*0)/(-2)=0
669. a) S10=b1*(q^9–1)/(q–1)=
=(-1/36)*511)/1=-511/36
б) S6=b1*(q^5–1)/(q–1)=
=(-1/27*242)/2=-121/27
в) S10=b1*(q^9–1)/(q–1)=
=(-1/36*(-513)/(-3)=-4,75
г) S6=b1*(q^5–1)/(q–1)=
=(-2/27*(-244)/(-4)=(488/27*(-4)=
=-122/27