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bài 1 : so sánh
3.2 . 15 / 64 - ( 4/5 + 2/5 ) =
3.2 . 15 / 64 - 6/5 =
3/ 4 - 6/ 5 = -9/20
vì -9/ 20 < 0
2/3 > 0
theo tính chất bắc cầu ta có : 2/ 3 > - 9 / 20
\(=\frac{16}{5}.\frac{-15}{64}-\left(\frac{4}{5}+\frac{2}{3}\right):3\frac{2}{3}=\frac{16}{5}.\frac{-15}{64}+\frac{-22}{15}:\frac{11}{3}=\frac{-3}{4}+\frac{-2}{5}=\frac{-23}{20}\)
\(\dfrac{-3}{2}\times\dfrac{-15}{64}+\left(0,8-2\dfrac{4}{5}\right):3\dfrac{2}{3}\\ =\dfrac{45}{128}+\left(-2\right)\times\dfrac{3}{11}\\ =\dfrac{45}{128}-\dfrac{6}{11}\\ =-\dfrac{273}{1408}\)
- 6/7.8/13+6/13.9/7-3/13.6/7
- (-3,2).15/64+(0,8-2 4/15):3 2/3
- 1,4.15/49-(4/5+2/3):2 1/5
/ là phân số
1.=6/7.8/13+6/7.9/13-3/13.6/7=6/7.(8/13+9/13-3/13)=6/7.14/13=12/13
\(\dfrac{1}{2}+\dfrac{3}{4}-\left(\dfrac{3}{4}-\dfrac{4}{5}\right)\)
=\(\dfrac{1}{2}+\dfrac{3}{4}-\dfrac{3}{4}+\dfrac{4}{5}\)
=\(\left(\dfrac{1}{2}+\dfrac{4}{5}\right)+\left(\dfrac{3}{4}-\dfrac{3}{4}\right)\)
=\(\left(\dfrac{5}{10}+\dfrac{8}{10}\right)+0\)
=\(\dfrac{13}{10}\)
\(-\dfrac{7}{25}.\dfrac{11}{13}+\left(-\dfrac{7}{25}\right).\dfrac{2}{13}-\dfrac{18}{25}\)
=\(-\dfrac{7}{25}.\cdot\left(\dfrac{11}{13}+\dfrac{2}{13}\right)-\dfrac{18}{25}\)
=\(-\dfrac{7}{25}.1-\dfrac{18}{25}\)
=\(-\dfrac{7}{25}-\dfrac{18}{25}\)
=\(-\dfrac{25}{25}\) = \(-1\)