Lula Nguyễn
20/08/2017 at 15:24-
Ngân Hà 20/08/2017 at 15:27\(A=\dfrac{2}{4.5}+\dfrac{2}{5.6}+\dfrac{2}{6.7}+...+\dfrac{2}{15.16}\)
\(A=2\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{15.16}\right)\)
\(A=2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{15}-\dfrac{1}{16}\right)\)
\(A=2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\)
\(A=2.\dfrac{3}{16}\)
\(A=\dfrac{6}{16}=\dfrac{3}{8}\)
Lula Nguyễn selected this answer. -
Ngân Hà 20/08/2017 at 15:37
What do you mean? I just rewrite the question! The one who asked is Lula Nguyễn, not me!
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Ngô Tấn Đạt 20/08/2017 at 15:34\(A=\dfrac{2}{4.5}+\dfrac{2}{5.6}+\dfrac{2}{6.7}+...+\dfrac{2}{15.16}\\ =2\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{15.16}\right)\\ =2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+....+\dfrac{1}{15}-\dfrac{1}{16}\right)\\ =2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)\\ =\dfrac{1}{2}-\dfrac{1}{8}=\dfrac{3}{8}\)
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Dao Trong Luan 20/08/2017 at 15:30\(A=2\left(\dfrac{1}{4\cdot5}+\dfrac{1}{5\cdot6}+...+\dfrac{1}{15\cdot16}\right)\)
\(=2\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{15}-\dfrac{1}{16}\right)\)
\(=2\left(\dfrac{1}{4}-\dfrac{1}{16}\right)=2\cdot\dfrac{3}{16}=\dfrac{3}{8}\)
Ngân Hà auto ask, auto answer.