\(\dfrac{a}{3}=\dfrac{b}{2};\dfrac{b}{6}=\dfrac{c}{5}\)
\(\Rightarrow\dfrac{a}{9}=\dfrac{b}{6};\dfrac{b}{6}=\dfrac{c}{5}\)

\(\Rightarrow\dfrac{a}{9}=\dfrac{b}{6}=\dfrac{c}{5}\)
Áp dụng tính chất của dãy tỉ số bằng nhau, ta có:
\(\dfrac{a}{9}=\dfrac{b}{6}=\dfrac{c}{5}=\dfrac{a+b+c}{9+6+5}=\dfrac{-40}{20}=-2\)
\(\Rightarrow\left\{{}\begin{matrix}a=-2\cdot9=-18\\b=-2\cdot6=-12\\c=-2\cdot5=-10\end{matrix}\right.\)

a)

x^2-16/25=0

x^2-4^2/5^2=0

=>x-4/5=0

x=0+4/5

x=0/5

a) 13,5                    b)-7,2

c)2,1                        d)407/96

\(a.\dfrac{5}{3}.8,1=\dfrac{40,5}{3}\)

\(b.\dfrac{8}{5}.\left(-4,5\right)=\dfrac{-36}{5}\)

\(c.\dfrac{14}{5}.75\%=\dfrac{10,5}{5}=2,1\)

\(d.\dfrac{11}{8}.\dfrac{37}{12}=\dfrac{407}{96}\)

a) \(1\dfrac{2}{3}.8,1=\dfrac{5}{3}.\dfrac{81}{100}=\dfrac{27}{20}\)

b) \(1\dfrac{3}{5}.\left(-4,5\right)=\dfrac{8}{5}.\left(-\dfrac{45}{10}\right)=-\dfrac{36}{5}\)

c) \(75\%.\dfrac{14}{5}=\dfrac{75}{100}.\dfrac{14}{5}=\dfrac{21}{10}\)

d) \(1\dfrac{3}{8}.3\dfrac{1}{12}=\dfrac{11}{8}.\dfrac{37}{12}=\dfrac{407}{96}\)

4 1/2 của 2/5kg là 9/5kg

2/5 của 40 là 16

5/6 của 48000 đồng là 40000 đồng

a)\(\frac{2}{5}\)của 40 = \(16\)

b)\(\frac{5}{6}\)của 48000 đồng = 40000 đồng

c)\(\frac{1}{2}\)của \(\frac{2}{5}\)kg = \(\frac{9}{5}\)kg

`#3107`

a)

\(\dfrac{11}{12}-\left(\dfrac{2}{5}+\dfrac{3}{4}x\right)=\dfrac{2}{3}?\\ \Rightarrow\dfrac{2}{5}+\dfrac{3}{4}x=\dfrac{11}{12}-\dfrac{2}{3}\\ \Rightarrow\dfrac{2}{5}+\dfrac{3}{4}x=\dfrac{1}{4}\\ \Rightarrow\dfrac{3}{4}x=\dfrac{1}{4}-\dfrac{2}{5}\\ \Rightarrow\dfrac{3}{4}x=-\dfrac{3}{20}\\ \Rightarrow x=-\dfrac{3}{20}\div\dfrac{3}{4}\\ \Rightarrow x=-\dfrac{1}{5}\)

Vậy, \(x=-\dfrac{1}{5}\)

b)

\(\dfrac{-2}{5}+\dfrac{5}{3}\cdot\left(\dfrac{3}{2}-\dfrac{4}{15}x\right)=\dfrac{-7}{6}\\ \Rightarrow\dfrac{5}{3}\cdot\left(\dfrac{3}{2}-\dfrac{4}{15}x\right)=\dfrac{-7}{6}-\dfrac{-2}{5}\\ \Rightarrow\dfrac{5}{3}\cdot\left(\dfrac{3}{2}-\dfrac{4}{15}x\right)=-\dfrac{23}{30}\\ \Rightarrow\dfrac{3}{2}-\dfrac{4}{15}x=-\dfrac{23}{30}\div\dfrac{5}{3}\\ \Rightarrow\dfrac{3}{2}-\dfrac{4}{15}x=-\dfrac{23}{50}\\ \Rightarrow\dfrac{4}{15}x=\dfrac{3}{2}-\left(-\dfrac{23}{50}\right)\\ \Rightarrow\dfrac{4}{15}x=\dfrac{49}{25}\\ \Rightarrow x=\dfrac{147}{20}\)

Vậy, \(x=\dfrac{147}{20}\)

c)

\(\dfrac{1}{2}+\dfrac{3}{4}x=\dfrac{1}{4}\\ \Rightarrow\dfrac{3}{4}x=\dfrac{1}{4}-\dfrac{1}{2}\\ \Rightarrow\dfrac{3}{4}x=-\dfrac{1}{4}\\ \Rightarrow x=-\dfrac{1}{4}\div\dfrac{3}{4}\\ \Rightarrow x=-\dfrac{1}{3}\)

Vậy, \(x=-\dfrac{1}{3}.\)

\(#Emyeu1aithatroi...\)

(2/5 + 3/4 . x)= 11/12 -2/3

(2/5 +3/4 . x)= 1/4

3/4 . x          = 1/4 - 2/5

3/4 . x          = -3/20

x                  = -3/20 : 3/4

x                  = -1/5

Vậy .....

a) 2/5 của 40 là

40 . 2/5 = 16

b) 5/6 của 48 000 đồng là

48 000 . 5/6 = 40 000 (đồng)

c) \(4\frac{1}{2}=\frac{9}{2}\)

\(\Rightarrow\frac{9}{2}\) của 2/5 kg là

2/5 . 9 /2 = 9/5 (kg)

A) \(40.\frac{2}{5}=16\)

B) \(48000.\frac{5}{6}=40000\left(đ\right)\)

C)\(\frac{2}{5}.4\frac{1}{2}=\frac{2}{5}.\frac{9}{2}=\frac{9}{5}\)(kg)

A. 40:5.2=16

B.48000:6.5=40000(đồng)

C. 2/5:2.41=9/5(kg)

Đặt \(\left(2\sqrt{a}-5;2\sqrt{b}-5;2\sqrt{c}-5\right)=\left(x;y;z\right)\Rightarrow\left\{{}\begin{matrix}x;y;z>0\\a=\left(\dfrac{x+5}{2}\right)^2\\b=\left(\dfrac{y+5}{2}\right)^2\\c=\left(\dfrac{z+5}{2}\right)^2\end{matrix}\right.\)

\(Q=\dfrac{\left(x+5\right)^2}{4y}+\dfrac{\left(y+5\right)^2}{4z}+\dfrac{\left(z+5\right)^2}{4x}\ge\dfrac{\left(x+y+z+15\right)^2}{4\left(x+y+z\right)}\)

\(Q\ge\dfrac{\left(x+y+z\right)^2+30\left(x+y+z\right)+225}{4\left(x+y+z\right)}\)

\(Q\ge\dfrac{x+y+z}{4}+\dfrac{225}{4\left(x+y+z\right)}+\dfrac{15}{2}\ge2\sqrt{\dfrac{225\left(x+y+z\right)}{16\left(x+y+z\right)}}+\dfrac{15}{2}=15\)

Dấu "=" xảy ra khi \(a=b=c=25\)

Áp dụng bđt hoán vị cho hai bộ số đơn điệu ngược chiều \(\left(a,b,c\right);\left(2\sqrt{a}-5,2\sqrt{b}-5,2\sqrt{c}-5\right)\): \(Q\ge\dfrac{a}{2\sqrt{a}-5}+\dfrac{b}{2\sqrt{b}-5}+\dfrac{c}{2\sqrt{c}-5}\).

Mặt khác ta có \(\dfrac{a}{2\sqrt{a}-5}-5=\dfrac{\left(\sqrt{a}-5\right)^2}{2\sqrt{a}-5}\ge0\).

Do đó \(Q\ge5+5+5=15\).

Dấu bằng xảy ra khi a = b = c = 25.

dễ v

a, 35

b, 1,35 tấn

c,0,28

\(a.\)

\(-\dfrac{2}{3}\cdot\dfrac{?}{4}=\dfrac{1}{2}\)

\(\Leftrightarrow\dfrac{?}{4}=\dfrac{1}{2}:-\dfrac{2}{3}=\dfrac{1}{2}\cdot-\dfrac{3}{2}=-\dfrac{3}{4}\)

\(\Leftrightarrow?=-3\)

\(b.\)

\(\dfrac{?}{3}\cdot\dfrac{5}{8}=-\dfrac{5}{12}\)

\(\Leftrightarrow\dfrac{?}{3}=\dfrac{-5}{12}:\dfrac{5}{8}=\dfrac{-5}{12}\cdot\dfrac{8}{5}=-\dfrac{2}{3}\)

\(\Leftrightarrow?=-2\)

\(c.\)

\(\dfrac{5}{6}\cdot\dfrac{3}{?}=\dfrac{1}{4}\)

\(\Leftrightarrow\dfrac{3}{?}=\dfrac{1}{4}:\dfrac{5}{6}=\dfrac{1}{4}\cdot\dfrac{6}{5}=\dfrac{3}{10}\)

\(\Leftrightarrow?=10\)

Mk gọi ? = x nha

a) \(\dfrac{-2}{3}.\dfrac{x}{4}=\dfrac{1}{2}\) 

           \(\dfrac{x}{4}=\dfrac{1}{2}:\dfrac{-2}{3}\) 

           \(\dfrac{x}{4}=\dfrac{-3}{4}\) 

⇒x=-3

b)\(\dfrac{x}{3}.\dfrac{5}{8}=\dfrac{-5}{12}\)  

       \(\dfrac{x}{3}=\dfrac{-5}{12}:\dfrac{5}{8}\) 

       \(\dfrac{x}{3}=\dfrac{-2}{3}\) 

⇒x=-2

c)\(\dfrac{5}{6}.\dfrac{3}{x}=\dfrac{1}{4}\) 

        \(\dfrac{3}{x}=\dfrac{1}{4}:\dfrac{5}{6}\) 

        \(\dfrac{3}{x}=\dfrac{3}{10}\) 

⇒x=10