Question

1 phần 1 x 2 x 3 + 1 phần 2 x 3 x 4 + 1 phần 3 x 4 x 5 + ... + 1 phần 37 x 38 x 39

Answer 1

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Answer 2

185/741

Answer 3

\(A=\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+....+\dfrac{1}{37.38.39}\)

\(A=\dfrac{1}{2}.\left(\dfrac{2}{1.2.3}+\dfrac{2}{2.3.4}+....+\dfrac{2}{37.38.39}\right)\)\(A=\dfrac{1}{2}\left(\dfrac{3-1}{1.2.3}+\dfrac{4-2}{2.3.4}+....+\dfrac{39-37}{37.38.39}\right)\)

\(A=\dfrac{1}{2}.\left(\dfrac{1}{1.2}-\dfrac{1}{2.3}+\dfrac{1}{2.3}-\dfrac{1}{3.4}+.....\right)\)