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\(\dfrac{-3}{5}+\dfrac{43}{10}+\dfrac{7}{6}-\dfrac{28}{15}\)
\(=3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{-3}{5}+\frac{28.43}{5.56}+\frac{28.5}{5.24}-\frac{28.21}{5.63}\)
=\(\frac{-3}{5}+\frac{2.2.7.43}{5.2.2.7.2}+\frac{2.2.7.5}{2.2.2.3.5}-\frac{2.2.7.3.7}{5.7.3.3}\)
=\(\frac{-3}{5}+\frac{43}{5.2}+\frac{7}{2.3}-\frac{28}{15}\)
=\(\frac{-3}{5}+\frac{43}{10}+\frac{7}{6}-\frac{28}{15}\)
=\(\frac{-18}{30}+\frac{129}{30}+\frac{35}{30}-\frac{56}{30}\)
=\(\frac{-18+129+35-56}{30}\)
=\(\frac{90}{30}=3\)
Chúc bn học tốt
![](https://rs.olm.vn/images/avt/0.png?1311)
b
.ta có
=-3/5+28/5.43/56+28/5.5/24-28/5.21/63
=-3/5+28/5.(43/56+5/24-21/63)
=5.9/14=45/14
suy ra
biểu thức b có giá trị là 45/14
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-3/5 + 28.43/5.56 + 28.5/5.24 - 28.21/5.63
=-3/5 + 28.43/5.28.2 + 4.7.5/5.4.6 - 28.21/5.3.21
=-3/5 + 43/10 + 7/6 - 28/15
=-18/30 + 129/30 + 35/30 - 56/30
=-12+129+35-56/30
=94/30=47/15
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Đề sai. câu đầu phải là \(\dfrac{1}{18.21}\) mới đúng.
Nếu câu đầu là \(\dfrac{1}{18.21}\) thì mik có cách làm sau :
\(\dfrac{1}{18.21}+\dfrac{1}{21.24}+\dfrac{1}{24.27}+...+\dfrac{1}{123.126}\)
= \(\dfrac{1}{3}.\left(\dfrac{3}{18.21}+\dfrac{3}{21.24}+\dfrac{3}{24.27}+...+\dfrac{3}{123.126}\right)\)
= \(\dfrac{1}{3}.\left(\dfrac{1}{18}-\dfrac{1}{21}+\dfrac{1}{21}-\dfrac{1}{24}+\dfrac{1}{24}-\dfrac{1}{27}+...+\dfrac{1}{123}-\dfrac{1}{126}\right)\)
= \(\dfrac{1}{3}.\left(\dfrac{1}{18}-\dfrac{1}{126}\right)\)
= \(\dfrac{1}{3}.\dfrac{1}{21}\)
= \(\dfrac{1}{63}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) `(-63)/72 = (-63:9)/(72:9)=(-7)/8`
b) `20/(-140) = (20:20)/(-140:20) = 1/(-7)=(-1)/7`
c) `(3.10)/(5.24) =(3.2.5)/(5.2 .3.4)=1/4`
d) `(6.5-6.2)/(6+3)=18/9=2`
\(\frac{-3}{5}+\frac{28}{5}.\left(\frac{21}{56}+\frac{5}{24}-\frac{21}{63}\right)\)
\(\frac{-3}{5}+\frac{28}{5}.\frac{1}{4}\)
\(\frac{-3}{5}+\frac{7}{5}\)
\(\frac{4}{5}\)
sai cái gì mong bạn thông cảm
\(\frac{-3}{5}+\frac{28\cdot21}{5\cdot56}+\frac{28\cdot5}{5\cdot24}-\frac{28\cdot21}{5\cdot63}\)
\(=\frac{-3}{5}+\frac{28.21}{5\cdot28\cdot2}+\frac{4\cdot7\cdot5}{5\cdot4\cdot6}-\frac{28\cdot21}{5\cdot21\cdot3}\)
\(=\frac{-3}{5}+\frac{21}{5\cdot2}+\frac{7}{6}-\frac{28}{5\cdot3}\)
\(=\frac{-3}{5}+\frac{21}{10}+\frac{7}{6}-\frac{28}{15}\)
\(=\frac{-36+126+70-112}{60}\)
\(=\frac{48}{60}=\frac{4}{5}\)