rozwiąż równanie
1+7+13+ 19+...+x=280
1+7+13+19+180+60=280 x=60
a1 = 1 , r = 6 , an = x , Sn = 280an = a1 + (n − 1)*rx = 1 + (n − 1)*6x = 1 + 6*n − 6
x=6n - 5
6n=-5 - x
n= (-5-x)/6
sn=n(a1+an)/2
280=1/12((5+x)(1+x) /*12
3360=5+5x+x+x^2
x^2+6x-3355=0
delta=36+13420=13456
pierwiastek delta = 116
x=-6-116/2 <0
x=-6+116/2=110/2 =55
x=55
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1+7+13+19+180+60=280 x=60
a1 = 1 , r = 6 , an = x , Sn = 280
an = a1 + (n − 1)*r
x = 1 + (n − 1)*6
x = 1 + 6*n − 6
x=6n - 5
6n=-5 - x
n= (-5-x)/6
sn=n(a1+an)/2
280=1/12((5+x)(1+x) /*12
3360=5+5x+x+x^2
x^2+6x-3355=0
delta=36+13420=13456
pierwiastek delta = 116
x=-6-116/2 <0
x=-6+116/2=110/2 =55
x=55