Question

4+7+10+13+...+40= Va rog Frumos rezolvatimio multumesc!

Answer 1

4+40=44
7+37=44
10+34=44
13+31=44
16+28=44
19+25=44
22 ramane fara pereche
44*6+22= 264+22=286

Answer 2

$4+7+10+13+...+40 \\ \\ 40=4+(n-1) \times 3 \\ \\ 40=4+3n-3 \\ \\ 3n=40-4+3 \\ \\ 3n=39 \\ \\ n=39:3 \\ \\ n=13$

$\displaystyle S_1_3= \frac{8+12 \times 3}{2} \times 13 \\ \\ S_1_3= \frac{8+36}{2} \times 13 \\ \\ S_1_3= \frac{44}{2} \times 13 \\ \\ S_1_3=22 \times 13 \\ \\ S_1_3=286$