S=1.2+2.3+...+39.40
3S=1.2.3+2.3.3+...+39.40.3
3S=1.2.(3-0)+2.3.(4-1)+...+39.40.(41-38)
3S=1.2.3-0.1.2+2.3.4-1.2.3+...+39.40.41-38.39.40
3S=(1.2.3+2.3.4+...+39.40.41)-(0.1.2+1.2.3+...+38.39.40)
3S=39.40.41-0.1.2
3S=39.40.41
S=\(\frac{39.40.41}{3}=21320\)
Tính: 1.2 + 2.3 + 3.4 + 4.5 + .........................+37.38 + 38.39 + 39.40
S=1.2+2.3+3.4+...+38.39+39.40
Tính : S = 1.2 + 2.3 + 3.4 + ... + 38.39 + 39.40
Tính: S=1.2+2.3+3.4+...+38.39+39.40
1.2+2.3+3.4+........+38.39+39.40
1.2+2.3+3.4+...+38.39+39.40
1.2+2.3+3.4.........+38.39+39.40=?
Tính S=1.2+2.3+3.4+...+38.39+39.40. Ai trả lời nhanh nhất mk chọn nha!
tính:
1.2+2.3+3.4+.........+38.39+39.40
