1. Oblicz sumę ośmiu początkowych wyrazów ciąu geometrycznego. a3=36 i a6=121,5.
3r=121,5-36
3r=85,5/:3
r=28,5
a3=a1+2r
a1=36-2*28,5=36-57
a1=-21
Sn(2a1+(n-1)*r)*n/2
S8=(-42+7*28,5)*4=-168+798=630
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3r=121,5-36
3r=85,5/:3
r=28,5
a3=a1+2r
a1=36-2*28,5=36-57
a1=-21
Sn(2a1+(n-1)*r)*n/2
S8=(-42+7*28,5)*4=-168+798=630