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12.5 . -5/7 + 9 3/4 - 1.5 . 5/7
\(=\frac{5}{7}.\left(-60\right)+\frac{39}{4}-5.\frac{5}{7}\)
\(=\frac{5}{7}.\left[\left(-60\right)-5\right]+\frac{39}{4}\)
\(=\frac{5}{7}.\left(-65\right)+\frac{39}{4}\)
\(=\frac{-325}{7}+\frac{39}{4}=\frac{-1027}{28}\)
học tốt
= 25/2 . -5/7+ 39/4 + -3/2 . 5/7 = -125/14 + 39/4 + -15/14 = ( -125/14 + -15/14 ) + 39/4 = -10 + 39/4 = -1/4
\(4^{11}.25^{11}\le2^n.5^n\le20^{12}.5^{12}\)
\(\Rightarrow\left(2^2\right)^{11}.\left(5^2\right)^{11}\le2^n.5^n\le\left(2^2.5\right)^{12}.5^{12}\)
\(\Rightarrow2^{22}.5^{22}\le2^n.5^n\le2^{24}.5^{24}\)
\(\Rightarrow\left(2.5\right)^{22}\le\left(2.5\right)^n\le\left(2.5\right)^{24}\)
\(\Rightarrow22\le n\le24\Rightarrow n\in\left\{22;23;24\right\}\left(n\in N\right)\)
Ta có 411.2511=(4.25)11=10011=1022
2n.5n=(2.5)n=10n
2012.512=(20.5)12=10012=1024
⇒ 1022≤10n<1024
⇒ 22≤n<24
⇒ nϵ {22;23}
Nếu `a/-7=b/5` thì:
`A.a/-7=b/5=`\(\dfrac{b-a}{-7-5}\)
`B.a/-7=b/5=`\(\dfrac{a-b}{-7=5}\)
`C.a/-7=b/5=`\(\dfrac{b-a}{5-7}\)
D.`a/-7=b/5=`\(\dfrac{b-a}{5+7}\)
`---`
Vì `a/-7=b/5`
Theo tính chất tỉ lệ thức `-> a/-7=b/5=`\(\dfrac{b-a}{5-\left(-7\right)}=\dfrac{b-a}{5+7}\)
`->` Đáp án `D.`
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5: \(=3-\dfrac{1}{4}+\dfrac{2}{3}-5+\dfrac{1}{3}+\dfrac{6}{5}-6+\dfrac{7}{4}-\dfrac{3}{2}\)
\(=3-5-6+\dfrac{-1}{4}+\dfrac{7}{4}+\dfrac{2}{3}+\dfrac{1}{3}+\dfrac{6}{5}-\dfrac{3}{2}\)
\(=-8+\dfrac{3}{2}+1+\dfrac{-3}{10}\)
\(=-7+\dfrac{15-3}{10}=-7+\dfrac{6}{5}=-\dfrac{29}{5}\)
6: \(=6-\dfrac{2}{3}+\dfrac{1}{2}-5-\dfrac{5}{3}+\dfrac{3}{2}-3+\dfrac{7}{3}-\dfrac{5}{2}\)
\(=6-5-3-\dfrac{2}{3}-\dfrac{5}{3}+\dfrac{7}{3}+\dfrac{1}{2}+\dfrac{3}{2}-\dfrac{5}{2}\)
\(=-2-\dfrac{1}{2}=-\dfrac{5}{2}\)
7: \(=\dfrac{5}{3}-\dfrac{3}{7}+9-2-\dfrac{5}{7}+\dfrac{2}{3}+\dfrac{8}{7}-\dfrac{4}{3}-10\)
\(=9-2-10+\dfrac{5}{3}+\dfrac{2}{3}-\dfrac{4}{3}+\dfrac{-3}{7}-\dfrac{5}{7}+\dfrac{8}{7}\)
=-3+1
=-2
8: \(=8-\dfrac{9}{4}+\dfrac{2}{7}+6+\dfrac{3}{7}-\dfrac{5}{4}-3-\dfrac{2}{4}+\dfrac{9}{7}\)
\(=8+6-3+\dfrac{2}{7}+\dfrac{3}{7}+\dfrac{9}{7}-1-\dfrac{2}{4}\)
\(=11+2-1-\dfrac{1}{2}\)
=11+1/2
=11,5
12,5 : (-7,5) + 1,5 : (-7,5)
= 12,5 . (-5/7) + 1,5 . (-5/7)
= (12,5 + 1,5) . (-5/7)
= 14 . (-5/7)
= -10
12.5 :(-7/5)+1.5:(-7/5)
=(12.5+1.5):(-7/5)
=14:(-7/5)
=-10