L = 4/8 .13 +4/13 . 18 + 4 / 18.23 + .............. + 4/ 253 . 258 giúp nhanh vs em tick cho 30 phút nữa đi học r
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đặt A là ...
\(\Leftrightarrow\dfrac{5}{4}A=\dfrac{5}{8.13}+\dfrac{5}{13.18}+\dfrac{5}{18.24}+...+\dfrac{5}{253.258}\)
\(\Leftrightarrow\dfrac{5}{4}A=\dfrac{13-8}{8.13}+\dfrac{18-13}{13.18}+...+\dfrac{258-253}{253.258}\)
\(\Leftrightarrow\dfrac{5}{4}A=\dfrac{1}{8}-\dfrac{1}{13}+\dfrac{1}{8}-\dfrac{1}{13}+...+\dfrac{1}{253}-\dfrac{1}{258}\)
\(\Leftrightarrow\dfrac{5}{4}A=\dfrac{1}{8}-\dfrac{1}{258}\)
\(\Leftrightarrow\dfrac{5}{4}A=\dfrac{250}{258.8}\)
\(\Rightarrow A=\dfrac{250}{258.8}.\dfrac{4}{5}=\dfrac{25}{258}\)
1/3.(4/13-9/11)+1/3.(9/13-4/22)
=1/3(4/13-9/11+9/13-2/11)
=1/3(4/13+9/13-9/11-2/11)
=1/3(1-1)
=1/3.0=0
a: =11/4+5/4-9/8
=4-9/8=32/8-9/8=23/8
b: \(=\dfrac{6}{7}\cdot\dfrac{7}{4}+\dfrac{5}{3}=\dfrac{3}{2}+\dfrac{5}{3}=\dfrac{9+10}{6}=\dfrac{19}{6}\)
c: \(=\dfrac{13}{18}\cdot\dfrac{9}{5}-1=\dfrac{13}{10}-1=\dfrac{3}{10}\)
d: \(=3+\dfrac{9}{4}\cdot\dfrac{5}{3}=3+\dfrac{45}{12}=\dfrac{81}{12}=\dfrac{27}{4}\)