Question

Ajutatima va rog
2+4+6+8+....+120=120×(120+1)÷2
5+10+15+....+225=225×(225+1)÷2
7+14+21+....+70=70×(70+1)÷2
6+12+18+....+66=66×(66+1)÷2
5+6+7+8+....+50=50×(50+1)÷2
10+11+12+....+33=33×(33+1)÷2

Answer 1

1.

2 + 4 + 6 + 8 +....+ 120 = 2 × ( 1 + 2 + 3 + 4+......+ 60) = 2 ×(60 × 61):2 = 60 × 61 =

2.

5 + 10 + 15 +....+ 225 = 5 × ( 1 + 2 + 3 + 4+......+ 45) = 5 × (45 × 46): 2 = 5175

3.

7 + 14 + 21 +....+ 70 = 7 × ( 1 + 2 + 3 + 4+......+ 35) = 7 × (35 × 36): 2 = 4410

4.

6 + 12 + 18 +....+ 66 = 6 × ( 1 + 2 + 3 + 4+......+ 11) = 6 × (11 × 12): 2 = 396

5.

5 + 6 + 7 + 8 +....+ 50 = ( 1 + 2 + 3 + 4+......+ 50) - ( 1 + 2 + 3 + 4) = (50 × 51):2 -10 = 1275 -10 = 1265

6.

10 + 11 + 12 +....+ 33 = ( 1 + 2 + 3 + 4+......+ 33) - ( 1 + 2 + 3 + 4...+9)=

= (33 × 34):2 -(9 × 10):2 = 561 - 45 = 516