a: =>4/x=y/21=4/7

=>x=7; y=21*4/7=12

b: x/7=9/y

=>xy=63

mà x>y

nên \(\left(x,y\right)\in\left\{\left(63;1\right);\left(21;3\right);\left(9;7\right);\left(-7;-9\right);\left(-3;-21\right);\left(-1;-63\right)\right\}\)

c: x/15=3/y

=>xy=45

mà x<y<0

nên \(\left(x,y\right)\in\left\{\left(-45;-1\right);\left(-15;-3\right);\left(-9;-5\right)\right\}\)

d: x/y=21/28=3/4

=>x/3=y/4=k

=>x=3k; y=4k(k\(\in Z\))

=>4/x=y/21=4/7

=>x=7; y=12

=2

y=2

nếu x=14 thì y=28:14=2

\(y\times\dfrac{3}{4}++y:\dfrac{4}{5}=28\)

\(y\times\dfrac{3}{4}+y\times\dfrac{5}{4}=28\)

\(y\times\left(\dfrac{3}{4}+\dfrac{5}{4}\right)=28\)

\(y\times\dfrac{8}{4}=28\)

\(y\times2=28\)

\(y=\dfrac{28}{2}\)

\(y=14\)

a) (y - 24) : 28 = 20

y - 24 = 20 x 28

y - 24 = 560 

y = 560 + 24 

y = 584

vậy y = ...

a. 

\(\left(y-24\right):28=20\)

\(\left(y-24\right)=560\)

\(y=584\)

b. \(13\times\left(y-6\right)=4\times y-6\)

\(13\times y-78=4\times y-6\)

\(9\times y=72\)
\(y=8\)
c.\(y\times3+y\times4+y:3+y:4=182\)

\(y\times\left(3+4\right)+y:\left(3+4\right)=182\)

\(y\times\left(7+\dfrac{1}{7}\right)=182\)

\(y=\dfrac{637}{25}\)

a: 4/x=y/21=28/29

=>x=4:28/29=29/7; y=28/29x21=588/29

b: x/y=21/28

nên x/y=3/4

=>4x=3y

Giúp mình với

\(\dfrac{x}{2}=\dfrac{y}{3};\dfrac{y}{4}=\dfrac{z}{5}\\ \Rightarrow\dfrac{x}{8}=\dfrac{y}{12}=\dfrac{z}{15}=\dfrac{x-y-z}{8-12-15}=-\dfrac{28}{19}\\ \Rightarrow\left\{{}\begin{matrix}x=\dfrac{-224}{19}\\y=\dfrac{-336}{19}\\z=\dfrac{-420}{19}\end{matrix}\right.\)

Ta có 

x/2=y/3; y/4=z/2

=> x/8=y/12;y/12=z/6                    ( vế trái chia mỗi p/s cho 4, vế phải chia mỗi p/s cho 3)

=>x/8=y/12=z/6=x-y-z=8-12-6=28/-10

=> x/8=-2,8=> x=8*-2,8=...

     y/12=-2,8=>y=12*-2,8=...

      z/6=-2,8=> z=6*-2,8=...

KL:

Ta có :

\(\frac{x}{2}=\frac{y}{3};\frac{y}{4}=\frac{z}{2}\Rightarrow\frac{x}{8}=\frac{y}{12}=\frac{z}{6}\)

Đặt \(\frac{x}{8}=\frac{y}{12}=\frac{z}{6}=k\Rightarrow\hept{\begin{cases}x=8k\\y=12k\\z=6k\end{cases}}\)

Ta có :

\(x-y-z=48\Leftrightarrow8k-12k-6k=48\)  

                             \(\Leftrightarrow k.\left(8-12-6\right)=48\)

                              \(\Leftrightarrow k.\left(-10\right)=48\)

                             \(\Rightarrow k=-4,8\)

\(\Rightarrow\hept{\begin{cases}\frac{x}{8}=-4,8\\\frac{y}{12}=-4,8\\\frac{z}{6}=-4,8\end{cases}\Rightarrow\hept{\begin{cases}x=-38,4\\y=-57,6\\z=-28,8\end{cases}}}\)

Vậy \(\hept{\begin{cases}x=-38,4\\y=-57,6\\z=-28,8\end{cases}}\)

NHỚ CHO MK NHA

x/2=y/3 nên x/8=y/12

y/4=z/5 nên y/12=z/15

=>x/8=y/12=z/15

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

x/8=y/12=z/15=(x-y-z)/(8-12-15)=28/-19

nên x=28/-19*8=-224/19

       y=28/-19*12=-336/19

       z=28/-19*15=-420/19

(hình như đề sai, mk nghĩ là bạn đánh lộn 38 thành 28, chứ số lớn wa)

x=-224/19

y=-336/19

z=-420/19

ko bt :)))))))