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Progresii aritmetice - exercitiu rezolvat 5

Sa se gaseasca primii doi termeni ai progresiei aritmetice (bn) data astfel:

b1, b2, 15, 21, 27, …….

notam: 

15 = b3
21 = b4
27 = b5

Aflam ratia r
b4 – b3 = r

21 – 15 = r

=> r = 6

Astfel primii 2 termeni sunt:

b2 = b3 – r => b2 = 15 – 6
=> b2 = 9

b1 = b2 – r => b1 = 9 – 6