Răspuns :
40 + 41 + 42 + ..... + 100 = 4 270
→ stabilesc cati termeni are suma cu ratia = 1
100 - 40 + 1 = 61 termeni are suma
= 61 × ( 40 + 100 ) : 2 =
= 61 × 140 : 2 =
= 61 × 70 =
= 4 270
1+2+3+...+100=(100×101)/2=50×101=5050
1+2+3+...+39=(39×40)/2=39×20=780
5050-780=4270
1+2+3+...+39=(39×40)/2=39×20=780
5050-780=4270