Question

Sa se determine suma primilor n termeni ai progresiei aritmetice a n daca : a 1 = 100 , r=2 , n=60 ?

Answer 1

S = a1 × n + r × $\frac{n(n-1)}{2}$
S = 100 x 60 + 2 x  $\frac{100 x 99}{2}$
S = 6000 + 2 x 9900
S = 6000 + 19800
S =25800