Question

1.2.3 cộng 2.3.4 cộng 3.4.5 cộng  ........ cộng 98.99.100

Answer 1

\(4A=1.2.3.4+2.3.4 \left(5-1\right)+3.4.5\left(6-2\right)+....+98.99.100\left(101-97\right)\)

\(4A=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+...+98.99.100.101-97.98.99.100\)

\(\Rightarrow4A=98.99.100.101=97990200\)

Answer 2

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