Question

Áp dụng tính tổng : S=1.2+2.3+4.5+...+99.100

Answer 1

=

Answer 2

\(S=1.2+2.3+..........+99.100\)

\(\Leftrightarrow3A=1.2.3+2.3.3+.........+99.100.3\)

\(\Leftrightarrow3A=1.2.\left(3-0\right)+2.3.\left(4-1\right)+...........+99.100.\left(101-98\right)\)

\(\Leftrightarrow3A=1.2.3+2.3.4-1.2.3+...........+99.100.101-98.99.100\)

\(\Leftrightarrow3A=\left(1.2.3-1.2.3\right)+\left(2.3.4-2.3.4\right)+........+\left(98.99.100-98.99.100\right)+99.100.101\)

\(\Leftrightarrow3A=\dfrac{99.100.101}{3}=333300\)

Answer 3

đề sai kìa