Ciągi arytmetyczne i ciągi geometryczne:
Zad 1)
a1=12
a2=8
Oblicz s20
Zad 2)
q=2
s10=3069
Oblicz a1
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Zad.1
a₁=12
a₂=8
r=8-10=-4
a(n)=a₁+(n-1)r=12+(n-1)-4
a(n)=12-4n+4=-4n+16
S(20)=(12-4n+16)n*1/2
S(20)=(12-80+16)40
s(20)=-2080
Zad.2
q=2
S10=3069
S(10)=a1(1-2¹⁰)/1-2
S(10)=a1(1-1024)/-1
S(10)=1023a1
3069=1023a1
a1=3