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2010-01-29T17:35:02+01:00
A1= 3
a2= 7
an= 3 +(n-1)4
an = 3 + 4n -4 = 4n -1

S= (3+4n-1)n/2
S=1081

2n²+n=1081
2n²+n-1081=0
√Δ= 93
n = (-1+93)4 = 23

a23= 4*23-1 = 91 = x
2010-01-29T17:41:53+01:00
A1= 3
a2= 7
an= 3 +(n-1)4
an = 3 + 4n -4 = 4n -1

S= (3+4n-1)n/2
S=1081

2n²+n=1081
2n²+n-1081=0
√Δ= 93
n = (-1+93)4 = 23

a23= 4*23-1 = 91 = x