Question

Cum rezolv :3+6+9+12+.........+57 ?

Answer 1

3×(1+2+3+...+19)=3×(19×20)/2=3×190=570

Answer 2

3 + 6 + 9 + 12 + ........... + 57 = 
3 • ( 1 + 2 + 3 + 4 + ........ + 19 ) =
3 • 19 • 20/2 = 
3 • 19 • 10 =
57 • 10 = 570