Question

[(9+18+27+.......+900)-(7+14+21+.......+700)]:(1+2+3+...100)Va rog

Answer 1

=[9(1+2+3+...+100)-7(1+2+3+...+100)] : (1+2+3+...+100)
=[(1+2+3+...+100)*(9-7)] :(1+2+3+...+100)
= (1+2+3+...+100)*2:(1+2+3+...+100)
=2

Answer 2

9+18+27+...+900=9*1+9*2+9*3+...+9*100
=9(1+2+3+...+100)
1+2+3+...+100=100*101=50*101=5050 (100 se împarte la 2)
2
=9*5050=45450

7+14+21+....+700=7*1+7*2+7*3+...+7*100
=7(1+2+3+...+100)
=7*5050
=35350

1+2+3+...+100=100*101=50*101=5050
2

45450-35350:5050=45443