A=1.2+2.3+3.4+...+38+39+39.40
3A= 1.2.3+2.3.3+3.4.3+...+38.39.3+39.40.3
=1.2.3+2.3.(4-1)+3.4.(5-1)+...+38.39.(40-37)+39.40.(41-58)
=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+38.39.40-37.38.39+39.40.41-38.39.40
=39.40.41=63960
=>A=\(\frac{63960}{3}\)=21320
Tính : S = 1.2 + 2.3 + 3.4 + ... + 38.39 + 39.40
Tính: S=1.2+2.3+3.4+...+38.39+39.40
Tính: 1.2 + 2.3 + 3.4 + 4.5 + .........................+37.38 + 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=?
S=1.2+2.3+3.4+...+38.39+39.40
S=1.2+2.3+3.4+4.5+...+38.39+39.40
Tính S=1.2+2.3+3.4+...+38.39+39.40. Ai trả lời nhanh nhất mk chọn nha!
