Question

tính hợp lí
\(\dfrac{9}{8}-\dfrac{1}{2}-\dfrac{1}{6}-\dfrac{1}{12}-\dfrac{1}{20}-\dfrac{1}{30}-\dfrac{1}{42}-\dfrac{1}{56}-\dfrac{1}{72}\)
HELPP ME,MAI MIK KTRA R,MÌNH CẢM ƠN NHIỀU LẮM LẮM LẮM

Answer 1

\(\dfrac{9}{8}-\dfrac{1}{2}-\dfrac{1}{6}-...........-\dfrac{1}{72}\)

\(=\dfrac{9}{8}-\left(\dfrac{1}{2}+\dfrac{1}{6}+..........+\dfrac{1}{72}\right)\)

\(=\dfrac{9}{8}-\left(\dfrac{1}{1.2}+\dfrac{1}{2.3}+.........+\dfrac{1}{8.9}\right)\)

\(=\dfrac{9}{8}-\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+..........+\dfrac{1}{8}-\dfrac{1}{9}\right)\)

\(=\dfrac{9}{8}-\left(1-\dfrac{1}{9}\right)\)

\(=\dfrac{9}{8}-\dfrac{8}{9}\)

\(=\dfrac{17}{72}\)

Answer 2

2=1.2

6=2.3

12=3.4

20=4.5

30=5.6

.....

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