a: Áp dụng tính chất của DTSBN, ta được:

\(\dfrac{x}{3}=\dfrac{y}{4}=\dfrac{z}{5}=\dfrac{x+y+z}{3+4+5}=\dfrac{180}{12}=15\)

=>x=45; y=60; z=75

b: 

 Áp dụng tính chất của DTSBN, ta được:

\(\dfrac{x}{3}=\dfrac{y}{4}=\dfrac{z}{5}=\dfrac{x+y-z}{3+4-5}=\dfrac{8}{2}=4\)

=>x=12; y=16; z=20

Áp dụng tính chất của dãy tỉ số bằng nhau, ta có:

a) \(\frac{x}{3} = \frac{y}{4} = \frac{z}{5} = \frac{{x + y + z}}{{3 + 4 + 5}} = \frac{{180}}{{12}} = 15\)

Vậy x = 3 . 15 = 45; y = 4 . 15 = 60; z = 5 . 15 = 75

b) \(\frac{x}{3} = \frac{y}{4} = \frac{z}{5} = \frac{{x + y - z}}{{3 + 4 - 5}} = \frac{8}{2} = 4\)

Vậy x = 3. 4 = 12; y = 4.4 = 16; z = 5.4 = 20

b: =>x/y=3/5

=>5x-3y=0

c: =>xy=-15

\(\Leftrightarrow\left(x,y\right)\in\left\{\left(1;-15\right);\left(-15;1\right);\left(-1;15\right);\left(15;-1\right);\left(3;-5\right);\left(-5;3\right);\left(-3;5\right);\left(5;-3\right)\right\}\)

d: =>xy=-33

\(\Leftrightarrow\left(x,y\right)\in\left\{\left(1;-33\right);\left(-33;1\right);\left(-1;33\right);\left(33;-1\right);\left(3;-11\right);\left(-11;3\right);\left(-3;11\right);\left(11;-3\right)\right\}\)

a) \(\frac{x}{y}=\frac{21}{35}\)

=> x : y = 21 : 35 

=> \(\frac{x}{35}=\frac{y}{21}\)

21/35=3/5=6/10=....

a)\(\frac{x}{y}=\frac{21}{35}\)= \(x.35=y.21\)=\(\frac{x}{21}=\frac{y}{35}\)=

bó tay nha 

Dễ thui : Ta có: x/y  = 28/35

28 : 7 / 35 : 7 = 4/5=8/10=12/15=16/20

\(\frac{x}{y}=\)\(\frac{4}{5}\)

k mk nha

4/5 = 28/35

\(\frac{x}{24}=\frac{-2}{3}\Leftrightarrow x=\frac{-2\times24}{3}=-16\)

\(\frac{y}{-18}=\frac{-2}{3}\Leftrightarrow y=\frac{-2\times-18}{3}=12\)

\(\frac{-28}{z}=\frac{-2}{3}\Leftrightarrow z=\frac{-28\times3}{-2}=42\)

\(\frac{-10}{t}=\frac{-2}{3}\Leftrightarrow t=\frac{-10\times3}{-2}=15\)

\(\frac{x}{24}=\frac{y}{-18}=\frac{-28}{z}=\frac{-10}{t}=\frac{-2}{3}\)

\(\Rightarrow t=-15\)

\(\Rightarrow z=42\)

\(\Rightarrow y=12\)

\(\Rightarrow x=-16\)

Ta có \(\frac{x}{24}=\frac{-2}{3}\)

\(\Rightarrow3x=-48\)

\(\Rightarrow x=-16\)

\(\frac{y}{-18}=\frac{-2}{3}\)

\(\Rightarrow3y=36\)

\(\Rightarrow y=12\)

\(\frac{-28}{z}=\frac{-2}{3}\)

\(\Rightarrow-2z=-84\)

\(z=42\)

\(\frac{-10}{t}=\frac{-2}{3}\)

\(\Rightarrow-2t=-30\)

\(\Rightarrow t=15\)

\(\frac{3}{x}=\frac{y}{35}=\frac{-36}{84}\)

ta rút gọn phân số : \(\frac{-36}{84}=\frac{-3}{7}\)

ta có : \(\frac{3}{x}=\frac{y}{35}=\frac{-3}{7}\)

\(\frac{3}{x}=\frac{-3}{7}\Rightarrow x=\frac{3.7}{\left(-3\right)}=-7\)

\(\frac{y}{35}=\frac{-3}{7}\Rightarrow y=\frac{35.\left(-3\right)}{7}=-15\)

                   \(\frac{3}{x}=\frac{y}{35}=\frac{-36}{84}\)

                \(\Rightarrow\frac{3}{x}=\frac{y}{35}=\frac{-3}{7}\)

           Ta có : \(\frac{3}{x}=\frac{y}{35}=\frac{-3}{7}\)

               \(\frac{3}{x}=\frac{-3}{7}\)

               \(\Rightarrow x=\frac{3.7}{-3}=-7\)

                \(\frac{y}{35}=\frac{-3}{7}\Rightarrow y=\frac{-3.35}{7}=-15\)

              Ủng hộ mk nha !!! ^_^

\(\frac{3}{x}=\frac{y}{35}=-\frac{36}{84}\)
Ta có: \(-\frac{36}{84}=-\frac{3}{7}\)
\(\frac{3}{x}=\frac{y}{35}=-\frac{3}{7}\)
\(\frac{3}{x}=\frac{-3}{7}\Rightarrow x=\frac{3\times7}{\left(-3\right)}=-7\)
\(\frac{y}{35}=\frac{-3}{7}\Rightarrow y=\frac{35\times\left(-3\right)}{7}=-15\)
Vậy, \(x=-7\)\(;\)\(y=-15\)