Question

Tính tổng A = 1.2+2.3+3.4+....+99.100+100.101

Answer 1

\(3A=1.2.3+2.3.\left(4-1\right)+...+100.101.\left(102-99\right)\)

\(3A=1.2.3+2.3.4-1.2.3+.......+100.101.102-99.100.101\)

\(3A=100.101.102\)

\(A=\frac{100.101.102}{3}\)

\(A=343400\)

Answer 2

3=1.2.3+2.3(4-1)+...+100.101(102-99)

3=1.2.3+2.3.4-1.2.3+.....+100.101.102-99.100.101

3=100.101.101

=100.101.102/3

=343400

mn ủng hộ ^--^