Question

6+11+16+21+....+506  determinati

Answer 1

6=5x1+1
11=5x2+1
16=5x3+1
.............
506=5x101+1
In concluzie, suma are 101 termeni. Acesti termeni sunt in progresie aritmetica ,cu ratia 5.
$S= \frac{(a_1+a_n)\cdot n}{2} = \frac{(6+506)\cdot 101}{2} =25856$