Question

si c) 5+10+15+20+....+2020. Va implorrrrrrr ajutati-ma. Dau coroana

Answer 1

c)5 factor comun ( toate nr se impart la 5)
5×1+5×2+5×3+5×4+....404×5
5×(1+2+3+4+....404)
5×404×(404+1):2
5×404×405 :2
5×163.620:2
5×81810
=409050
b)4+8+12....+2020
- 4 factor comun
4×1+4×2+4×3.....+505
4×505×(505+1):2
4×505×506:2
4×255.530:2
4×127.765
=511.060
d)7+14+21+...+2023
- 7 factor comun
7×1+7×2+7×3+....289×7
7×(1+2+3+...289)
7×289×(289+1):2
7×289×290:2
7×83.810:2
7×41.905
=293.335