`a,` Áp dụng t/c dãy tỉ số bằng nhau ta có :

`x/2=y/3=z/4 = (x+y+z)/(2+3+4)=-18/9 =-2`

`=> x/2=-2=>x=-2*2=-4`

`=>y/3=-2=>y=-2*3=-6`

`=>z/4=-2=>z=-2*4=-28`

`b,` Áp dụng t/c dãy tỉ số bằng nhau ta có :

`x/5 =y/6=z/7 = (x-y+z)/(5-6+7)=36/6=6`

`=>x/5=6=>x=6*5=30`

`=>y/6=6=>y=6*6=36`

`=>z/7=6=>z=6*7=42`

`@ Kidd`

1/2-(2/3.x-1/3)=2/3

1/2-2/3x+1/3=2/3

1/2-2/3x=2/3-1/3

1/2-2/3x=1/3

2/3x=1/2-1/3

2/3x=1/6

x=1/6:2/3

x=1/4

vậy x bằng 1/4

Do \(EF>DF>DE\)

\(\Rightarrow\widehat{D}>\widehat{E}>\widehat{F}\) (góc đối diện với cạnh lớn hơn thì lớn hơn)

a) \(\dfrac{x}{-15}=\dfrac{-60}{3}\)

\(\Rightarrow x:\left(-15\right)=-20\)

\(\Rightarrow x=-20\cdot\left(-15\right)\)

\(\Rightarrow x=300\)

b) \(\dfrac{3,5}{15}=\dfrac{-2}{x}\)

\(\Rightarrow3,5\cdot x=-2\cdot15\)

\(\Rightarrow3,5x=-30\)

\(\Rightarrow x=-30:3,5\)

\(\Rightarrow x=-\dfrac{60}{7}\)

a: \(\dfrac{x}{-15}=-\dfrac{60}{3}\)

=>\(\dfrac{x}{15}=\dfrac{60}{3}\)

=>\(\dfrac{x}{15}=20\)

=>\(x=20\cdot15=300\)

b: \(\dfrac{3.5}{15}=\dfrac{-2}{x}\)

=>\(x=\dfrac{15\cdot\left(-2\right)}{3,5}=-\dfrac{30}{3,5}=-\dfrac{60}{7}\)

a)

\(\dfrac{x}{-15}=\dfrac{-60}{3}\\ \\ \\ \\ \Rightarrow\dfrac{x}{-15}=-20\\ \\ \\ \\ \Rightarrow x=-20.\left(-15\right)=300\)

Vậy x=300

b)

\(\dfrac{3,5}{15}=\dfrac{-2}{x}\\ \\ \\ \\ \Rightarrow x=-2:\dfrac{3,5}{15}=-\dfrac{30}{3,5}=-\dfrac{300}{35}=-\dfrac{60}{7}\)

Vậy x=\(-\dfrac{60}{7}\)

a: \(\dfrac{8}{12}:\dfrac{4}{15}=\dfrac{8}{12}\cdot\dfrac{15}{4}=\dfrac{120}{48}=\dfrac{5}{2}\)

b: \(\dfrac{0.75}{2.5}=\dfrac{75}{250}=\dfrac{3}{10}\)

\(\left(-10\right)\cdot20=\left(-25\right)\cdot8\)

=>\(\dfrac{-10}{-25}=\dfrac{8}{20};\dfrac{-10}{8}=\dfrac{-25}{20};\dfrac{-25}{-10}=\dfrac{20}{8};\dfrac{8}{-10}=\dfrac{20}{-25}\)

Khi có 36g nho khô thì khối lượng bột bánh cần tới là:

\(15:100\cdot36=0,15\cdot36=5,4\left(g\right)\)

Áp dụng t/c dãy tỉ số bằng nhau:

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

\(\Rightarrow\left\{{}\begin{matrix}x=-3.2=-6\\y=-3.3=-9\end{matrix}\right.\)