Question

Sa se scrie suma S= x1 + x6 + x11 + ... + x201 folosind simbolul ∑

Answer 1

.........................................................

Answer 2

$S = x_1 + x_6 + x_{11}+...+x_{201} \\ \\ S = \sum\limits_{k=0}^{40} x_{1+5k} \\ \\ S = \sum\limits_{k=1}^{41} x_{1+5(k-1)} \\ \\ S =\sum\limits_{k=1}^{41} x_{1+5k-5} \\ \\ S = \sum\limits_{k=1}^{41} x_{5k-4}$