Question

E=1.2.3+2.3.4+3.4.5+....+40.41.42

Tính E

Answer 1

4E = 1.2.3.4 + 2.3.4.4 + 3.4.5.4 + ... + 40.41.42.4

4E = 1.2.3.4 + 2.3.4.( 5 - 1 ) + 3.4.5.( 6 - 2 ) + .. + 40.41.42.( 43 - 39 )

4E = 1.2.3.4 + 2.3.4.5 - 1.2.3.4.+ 3.4.5.6 - 2.3.4.5 + .. + 40.41.42.43 - 39.40.41.42

4E = 40.41.42.43

E = 10 . 41 . 42 . 43 = 740640

Answer 2

4E = 1. 2 . 3 .4 + 2 . 3 . 4. 4 + 3. 4 . 5. 4 + ...+40 . 41. 42 . 4

4E = 1 . 2. 3. 4 + 2 . 3 . 4. 5 - 2. 3 .4 + 3 . 4. 5 . 6 - 3 . 4. 5 . 2  + ...+ 40 . 41. 42 . 43 - 40 . 41. 42 . 39

4E = 40 . 41. 42. 43 

  E = (40 . 41. 42. 43) : 4

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