Aici ai de a face scu progresii aritmetice
[tex]s = \frac{(a(0) + a(n)) \times r}{2} [/tex]
r-pasul progresiei
a)progresie aritmetică cu pasul 2
[tex]s = \frac{(1 + 2n + 1)2}{2} = 2n + 2[/tex]
b)pasul 4
[tex]s = \frac{(1 + 2n + 1)4}{2} = 4n + 4[/tex]
c)pasul -3
[tex]s = \frac{(2x + 2x - 3n + 3) \times (- 3)}{2} = \frac{12x + 9n - 9}{2} [/tex]
