Question

Tính:

\(A=1.2.3.4.5+2.3.4.5.6+3.4.5.6.7+..........+46.47.48.49.50\)

Answer 1

  A = 1.2.3.4.5 + 2.3.4.5.6 + 3.4.5.6.7 +...+ 46.47.48.49.50

6A = 1.2.3.4.5.(6-0) + 2.3.4.5.6.(7-1) + 3.4.5.6.7.(8-2) +...+ 46.47.48.49.50.(51-45)

6A = (1.2.3.4.5.6 + 2.3.4.5.6.7 + 3.4.5.6.7.8 +...+ 46.47.48.49.50.51) - (0.1.2.3.4.5 + 1.2.3.4.5.6 + 2.3.4.5.6.7 +...+ 45.46.47.48.49.50)

6A = 46.47.48.49.50.51 - 0.1.2.3.4.5

6A = 46.47.48.49.50.51

6A = 12966811200

  A = 12966811200 : 6

  A = 2161135200

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