W pewnym ciągu arytmetycznym a3=1 i a7=13 a)oblicz pierwszy wyraz i różnicę tego ciągu b)oblicz sumę stu początkowych wyrazów tego ciągu
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a3=1
a7=13
1=a1+2r
13=a1+6r
a1=1-2r
a1=13-6r
1-2r=13-6r
-2r+6r=13-1
4r=12
r=3
a1=1-6=-5
a1=-5
r=3
S100=[(a1+(n-1)r)/2] *100
S100=[(-5+99r)/2]*100
S100=[(-5+99*3)/2]*100
S100=[292/2]*100
S100=14600
licze na naj
a3+4r = a7
1+4r = 13
4r = 13-1
4r = 12 |:4
r = 3
a1+2r = a3
a1+2*3 = 1
a1 = 1-6
a1 = -5
a100 = a1+99r
a100 = -5+99*3
a100 = -5+297
a100 = 292
Sn = (a1+an)/2 * n
S100 = (a1+a100)/2 * 100
S100 = (-5+292)/2*100 = 287/2 * 100 = 143,5*100 = 14350