Wyznacz wzór ogolny ciągu arytmetycznego w którym a5= -7, a11= 11
Oblicz sumę a1 + a2 + ... + a2005.
a₅=-7 a₁₁=11
11=a₁+10r
-7=a₁+4r
-11=-a₁-10r
-18=-6r
r=3
a1=-19
an=-19+3n-3
an=3n-22
S2005=[2*(-19)+(2005-1)3]2005/2=[-38+6012]1002,5=5988935
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a₅=-7 a₁₁=11
11=a₁+10r
-7=a₁+4r
-11=-a₁-10r
-18=-6r
r=3
a1=-19
an=-19+3n-3
an=3n-22
S2005=[2*(-19)+(2005-1)3]2005/2=[-38+6012]1002,5=5988935