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â, -4/9(7/15+8/15)=-4/9
b,-5/4(16/25+9/25)=-5/4
,.....
dài quá mik làm ko hết
hok tốt
a)\(\frac{-4}{9}\times\frac{7}{15}+\frac{-4}{9}\times\frac{8}{15}\)
= \(\frac{-4}{9}\times\left(\frac{7}{15}+\frac{8}{15}\right)\)
=\(-\frac49\times1\)
=\(-\frac49\)
Bài 1:
a) b) c) sẽ có bạn giải cho em thôi vì nó dễ tính tay cũng đc
d) \(\frac{4}{2.5}+\frac{4}{5.8}+...+\frac{4}{23.26}\)
\(=\frac{4}{3}.\left(\frac{3}{2.5}+\frac{3}{5.8}+...+\frac{3}{23.26}\right)\)
\(=\frac{4}{3}.\left(\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+...+\frac{1}{23}-\frac{1}{26}\right)\)
\(=\frac{4}{3}.\left(\frac{1}{2}-\frac{1}{26}\right)\)
\(=\frac{4}{3}.\frac{6}{13}\)
\(=\frac{8}{13}\)
Bài 2:
a) b) c)
d)\(|\frac{5}{8}x+\frac{6}{7}|-\frac{4}{7}=\frac{10}{7}\)
\(\Leftrightarrow|\frac{5}{8}x+\frac{6}{7}|=2\)
\(\Leftrightarrow\orbr{\begin{cases}\frac{5}{8}x+\frac{6}{7}=2\\\frac{5}{8}x+\frac{6}{7}=-2\end{cases}}\)\(\Leftrightarrow\orbr{\begin{cases}\frac{5}{8}x=\frac{8}{7}\\\frac{5}{8}x=\frac{-20}{7}\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{64}{35}\\x=\frac{-32}{7}\end{cases}}}\)
Vậy \(x\in\left\{\frac{64}{35};\frac{-32}{7}\right\}\)
Bài 1 :
a) \(\left(\frac{2}{5}-\frac{5}{8}\right):\frac{11}{30}+\frac{1}{8}\)
\(=\frac{-9}{40}:\frac{11}{30}+\frac{1}{8}\)
\(=\frac{-27}{44}+\frac{1}{8}\)
\(=\frac{-43}{88}\)
Câu a:
- \(\frac{15}{8}\) + \(\frac78-4\)
= - \(\frac88\) - 4
= - 1 - 4
= - 5
Câu b:
- \(\frac57\).\(\frac{2}{11}\) \(-\frac57\).\(\frac{9}{11}\) + \(\frac67\)
= - \(\frac57\).(\(\frac{2}{11}\) + \(\frac{9}{11}\)) + \(\frac67\)
= - \(\frac57\). 1 + \(\frac67\)
= - \(\frac57\) + \(\frac67\)
= - \(\frac17\)
Câu 3 : \(2+4+6+.........+2n=156\)
\(\Leftrightarrow2\left(1+2+3+.....+n\right)=156\)
\(\Leftrightarrow1+2+3+.........+n=78\)
\(\Leftrightarrow\frac{n\left(n+1\right)}{2}=78\)\(\Leftrightarrow n\left(n+1\right)=156=12.13\)\(\Leftrightarrow n=12\)
Vậy \(n=12\)
Mk chỉ biết câu a thôi
a) \(\frac{\frac{5}{7}+\frac{5}{9}-\frac{5}{11}}{\frac{15}{7}+\frac{15}{9}-\frac{15}{11}}\)
= \(\frac{5\cdot\left(\frac{1}{7}+\frac{1}{9}-\frac{1}{11}\right)}{15\cdot\left(\frac{1}{7}+\frac{1}{9}-\frac{1}{11}\right)}\)
= \(\frac{5}{15}\)
= \(\frac{1}{3}\)
Chúc bạn học tốt
=1/1-1/2+1/2-1/3+1/3-1/4+.........+1/1999-1/2000
=1/1-1/2000
=1999/2000<3/4
\(\frac{-7}{11}.\frac{11}{19}+\frac{-7}{11}.\frac{8}{19}+\frac{-4}{11}\)
\(=\frac{-7}{11}.\left(\frac{11}{19}+\frac{8}{19}\right)+\frac{-4}{11}\)
\(=\frac{-7}{11}.1+\frac{-4}{11}\)
\(=\frac{-7}{11}+\frac{-4}{11}=\frac{-11}{11}=-1\)
~ Hok tốt ~
Đặt \(B=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\)
\(\Rightarrow B=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\)
\(\Rightarrow B=1-\frac{1}{2019}\)
\(\Rightarrow B=\frac{2018}{2019}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\)
\(=1+\left(\frac{1}{2}-\frac{1}{2}\right)+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{4}-\frac{1}{4}\right)+...+\left(\frac{1}{2018}-\frac{1}{2018}\right)-\frac{1}{2019}\)
\(=1-\frac{1}{2019}=\frac{2018}{2019}\)
~ Hok tốt ~
\(\left(4\frac{1}{9}+3\frac{1}{4}\right).2\frac{1}{4}+2\frac{3}{4}\)
\(=\left(\frac{37}{9}+\frac{13}{4}\right).\frac{9}{4}+\frac{11}{4}\)
\(=\frac{265}{36}.\frac{9}{4}+\frac{11}{4}\)
\(=\frac{265}{16}+\frac{11}{4}\)
\(=\frac{309}{16}\)
~ Hok tốt ~
-7/11.11/19+-7/11.8/19+-4/11
=-7/11.(11/19+8/19)+-4/11
=-7/11.19/19+-4/11
=-7/11+-4/11
=-11/11=-1
(4 1/9+3 1/4).2 1/4+2 3/4
=(37/9+13/4).9/4+11/4
=265/36.5/1
=1325/36
a)\(-\frac{7}{11}\cdot\frac{11}{19}+\frac{-7}{11}\cdot\frac{8}{19}+\frac{-4}{11}\)
\(=-\frac{7}{11}\left(\frac{11}{19}+\frac{8}{19}\right)+-\frac{4}{11}=-\frac{7}{11}\cdot\frac{19}{19}+-\frac{4}{11}\)
\(=\frac{-7}{11}\cdot1+\frac{-4}{11}=\frac{-11}{11}=-1\)
b)\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{2018\cdot2019}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\)
\(=1-\frac{1}{2019}=\frac{2018}{2019}\)
c) \(\left(\frac{1}{9}+3\frac{1}{4}\right)\cdot2\frac{1}{4}+2\frac{3}{4}\)
\(\left(\frac{37}{9}+\frac{13}{4}\right)\cdot\frac{9}{4}+\frac{11}{4}=\frac{37}{9}\cdot\frac{9}{4}+\frac{13}{4}\cdot\frac{9}{4}+\frac{11}{4}\)
\(=\frac{37}{4}+\frac{117}{16}+\frac{11}{4}=\frac{37}{4}+\frac{11}{4}+\frac{117}{16}=\frac{48}{4}+\frac{117}{16}\)
\(=\frac{192}{16}+\frac{117}{16}=\frac{309}{16}\)
hk tốt #
1/1.2+1/2.3+1/3.4....+1/2018.2019
=1-1/2+1/2-1/3+1/3-1/4...+1/2018-1/2019
=1+(1/2-1/2)+(1/3-1/3)....+(1/2018-1/2018)-1/2019
=1+1/2019
=2018/2019
\(-\frac{7}{11}.\frac{11}{19}+-\frac{7}{11}.\frac{8}{19}+-\frac{4}{11}\)
\(=-\frac{7}{11}.\left(\frac{11}{19}+\frac{8}{19}\right)+-\frac{4}{11}\)
\(=-\frac{7}{11}.1+\frac{-4}{11}\)
\(=-1\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\)
\(=1-\frac{1}{2019}\)
\(=\frac{2018}{2019}\)
\(\left(4\frac{1}{9}+3\frac{1}{4}\right).2\frac{1}{4}+2\frac{3}{4}\)
\(=\left(\frac{37}{9}+\frac{13}{4}\right).\frac{9}{4}+\frac{11}{4}\)
\(=\frac{265}{36}.\frac{9}{4}+\frac{11}{4}\)
\(=\frac{265}{16}+\frac{11}{4}\)
\(=\frac{309}{16}\)
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