Question

Anh chị giúp em với. Em cần gấp lắm.

Answer 1

\(C=\dfrac{2\cdot3-1}{1\cdot2\cdot3}+\dfrac{4\cdot5-1}{1\cdot2\cdot3\cdot4\cdot5}+...+\dfrac{14\cdot15-1}{1\cdot2\cdot...\cdot15}\\ C=1-\dfrac{1}{1\cdot2\cdot3}+\dfrac{1}{1\cdot2\cdot3}-\dfrac{1}{1\cdot2\cdot3\cdot4\cdot5}+\dfrac{1}{1\cdot2\cdot3\cdot4\cdot5}-...-\dfrac{1}{1\cdot2\cdot...\cdot13}-\dfrac{1}{1\cdot2\cdot...\cdot15}\\ C=1-\dfrac{1}{1\cdot2\cdot...\cdot15}< 1\)