\(\frac{4}{x-3}\)=\(\frac{8}{y-6}\)=\(\frac{20}{z-15}\)

=> \(\frac{x-3}{4}\)=\(\frac{y-6}{8}\)=\(\frac{z-15}{20}\)

=> \(\frac{x}{4}\)-\(\frac{3}{4}\)= \(\frac{y}{8}\)-\(\frac{6}{8}\)=\(\frac{z}{20}\)-\(\frac{15}{20}\)

=> \(\frac{x}{4}\)=\(\frac{y}{8}\)=\(\frac{z}{20}\)

Đặt \(\frac{x}{4}\)=\(\frac{y}{8}\)=\(\frac{z}{20}\)=k

\(\frac{x}{4}\)= k => x = 4 . k

\(\frac{y}{8}\)= k => y = 8 . k

\(\frac{z}{20}\)= k => z = 20 . k

Mà x.y.x = 640

(4k) . (8k) . (20k)= 640

640 . kmũ3 = 640

k mũ 3 = 640:640

k mũ 3 = 1

\(\frac{x}{4}\)= 1 => x = 4 . 1 = 4

\(\frac{y}{8}\)= 1 => y = 8 . 1 = 8

\(\frac{z}{20}\)= 1 => z = 20 . 1=20

Vậy x=4, y=8, z=20

k mình nha,đúng 100%

Ta có:\(\frac{4}{x-3}=\frac{8}{y-6}=\frac{20}{z-15}\)

=>\(\frac{x-3}{4}=\frac{y-6}{8}=\frac{z-15}{20}\)

=>\(\frac{x}{4}-\frac{3}{4}=\frac{y}{8}-\frac{6}{8}=\frac{z}{20}-\frac{15}{20}\)

=>\(\frac{x}{4}-\frac{3}{4}=\frac{y}{8}-\frac{3}{4}=\frac{z}{20}-\frac{3}{4}\)

=>\(\frac{x}{4}=\frac{y}{8}=\frac{z}{20}\)

Đặt \(\frac{x}{4}=\frac{y}{8}=\frac{z}{20}=k\Rightarrow x=4k,y=8k,z=20k\)

Thay vào đề ta có: xyz = 640

=> 4k.8k.20k = 640

=> 640k³ = 640

=> k³ = 1

=> k = 1

=> x = 4, y = 8, z = 20

Vậy...

bài 1 : a,ta có 3/x-1 =4/y-2=5/z-3 =>  x-1/3=y-2/4=z-3/5 

áp dụng .... => x-1+y-2+z-3 / 3+4+5 = x+y+z-1-2-3/3+4+5 = 12/12=1

do x-1/3 = 1 => x-1 = 3 => x= 4 ( tìm y,z tương tự

Bài 1: 

a) Ta có: 3/x - 1 = 4/y - 2 = 5/z - 3 => x - 1/3 = y - 2/4 = z - 3/5 áp dụng ... =>x - 1 + y - 2 + z - 3/3 + 4 + 5 = x + y + z - 1 - 2 - 3/3 + 4 + 5 = 12/12 = 1 do x - 1/3 = 1 => x - 1 = 3 => x = 4 ( tìm y, z tương tự )

cũng dễ thôi

\(a,\text{Ta có: }\frac{x}{3}=\frac{y}{9}=\frac{z}{5}=\frac{xyz}{3.9.5}=\frac{45}{45}=1\left(\text{T/c dãy tỉ số bằng nhau}\right).\)

\(\Rightarrow\frac{x}{3}=1\text{ Vậy }x=3\)

\(\Rightarrow\frac{y}{9}=1\text{ Vậy }y=9\)

\(\Rightarrow\frac{z}{5}=1\text{ Vậy }z=5\)

\(b,\text{Ta có: }\frac{x}{6}=\frac{y}{8}=\frac{z}{6}=\frac{x+y+z}{6+8+6}=\frac{24}{20}=\frac{6}{5}\left(\text{T/c dãy tỉ số bằng nhau}\right)\)

\(\Rightarrow\frac{x}{6}=\frac{6}{5}\text{ Vậy }x=\frac{36}{5}\)

\(\Rightarrow\frac{y}{8}=\frac{6}{5}\text{ Vậy }y=\frac{48}{5}\)

\(\Rightarrow\frac{z}{6}=\frac{6}{5}\text{ Vậy }z=\frac{36}{5}\)

Sr lúc nãy lm hơi vội ý a)

lm lại nha!! 

Ta có: x/3=y/9=z/5=xyz/3.9.5=45/135=1/3 (T/c dãy tỉ số bằng nhau)

 =>x/3=1/3, vậy x= 1

=>y/9=1/3, vậy  y=3

=>z/5=1/3,  vậy z= 5/3

đặt \(\frac{x}{3}=\frac{y}{4}=\frac{z}{6}=k\Rightarrow x=3k;y=4k;z=6k\)

thay x=3k;y=4k;z=6k vào x.y.z=576 ta được:

3k.4k.6k=576

72k³=576

k³=576:72

k³=8

k³=2³

=>k=2

=>x=3.2=6

y=4.2=8

z=6.2=12

Ta co :\(\frac{x}{3}=\frac{y}{4}=\frac{z}{6}\)  va x.y.z = 576

Dat :\(\frac{x}{3}=\frac{y}{4}=\frac{z}{6}=k\)

x=3k

y=4k

z=6k

x.y.z=72k³

576  =72k³

k³    = 8

=>k =2

Voi : k=2 \(\Rightarrow x=2.3=6;y=2.4=8;z=2.6=12\)

\(\)

??

Đặt \(\dfrac{x}{40}=\dfrac{y}{20}=\dfrac{z}{28}=k\Leftrightarrow x=40k;y=20k;z=28k\)

\(xyz=22400\\ \Leftrightarrow22400k^3=22400\\ \Leftrightarrow k^3=1\Leftrightarrow k=1\\ \Leftrightarrow\left\{{}\begin{matrix}x=40\\y=20\\z=28\end{matrix}\right.\)

\(\dfrac{x}{40}=\dfrac{y}{20}=\dfrac{z}{28}=k\)

\(\Rightarrow\left\{{}\begin{matrix}x=40k\\y=20k\\z=28k\end{matrix}\right.\)\(\Rightarrow xyz=22400k^3=22400\Rightarrow k=1\)

\(\Rightarrow\left\{{}\begin{matrix}x=40\\y=20\\z=28\end{matrix}\right.\)