Ta co: 18/x=2/5

nen 18.5=x.2

suy ra x.2=90

suy ra x= 90:2=45

Ta co: y/35=2/5 nen y.5=35.2

suy ra x.5=70

 suy ra x=70:5=14

Ta co:-8/z=2/5 nen -8.5=z.2

suy ra z.2=-40

suy ra z=-40:2=-20

hoctot!

\(\dfrac{x}{4}=\dfrac{18}{x+1};x^2+1=72\)

\(\)\(\Rightarrow x\left(x+1\right)=18.4\)

\(\Rightarrow x^2+x=72\)

\(\Rightarrow\left\{{}\begin{matrix}x^2+1=72\\x^2+x=72\end{matrix}\right.\)

\(\Rightarrow x^2+1=x^2+x\)

\(\Rightarrow x=1\)

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giúp mình với ạ mình cần gấp

a) Ta có: \(\dfrac{x}{2}=\dfrac{y}{5}\)

⇒\(\dfrac{y-x}{5-2}=\dfrac{6}{3}=2\)

\(\dfrac{x}{2}=2\Rightarrow x=4\)

\(\dfrac{y}{5}=2\Rightarrow y=10\)

\(\dfrac{z}{10}=2\Rightarrow z=20\)

b) Ta có: \(\dfrac{x}{8}=\dfrac{2y}{6}=\dfrac{z}{7}\)

\(\dfrac{x-2y+z}{8-6+7}=\dfrac{18}{9}=2\)

\(\dfrac{x}{8}=2\Rightarrow x=16\)

\(\dfrac{y}{3}=2\Rightarrow y=6\)

\(\dfrac{z}{7}=2\Rightarrow z=14\)

a)\(x.x=\frac{y}{-3}.\frac{y}{-3}=\frac{z}{4}.\frac{z}{4}=\frac{x^2+y^2-z^2}{1+9-16}=\frac{6}{-6}=-1\)

không tồn tại vì x.x>=0

b)\(\frac{x}{5}=\frac{y}{2}\Rightarrow\frac{x}{15}=\frac{y}{6}\)

\(\frac{x}{5}=\frac{y}{2}\Rightarrow\frac{z}{8}=\frac{y}{6}\)

Suy ra \(\frac{x}{15}=\frac{y}{6}=\frac{z}{8}=\frac{x-y+z}{15-6+8}=\frac{10}{17}\)

\(x=15.\frac{10}{17}=\frac{150}{17}\)

\(y=6.\frac{10}{17}=\frac{60}{17}\)

c) \(\frac{x}{5}=\frac{y}{3}=\frac{x-y}{5-3}=\frac{14}{2}=7\)

x=7.5=35; y=3.7=21

d) \(\frac{x}{2}=\frac{y}{5}\Rightarrow\frac{2x}{4}=\frac{y}{5}=\frac{2x+y}{4+5}=\frac{18}{9}=2\)

x=2.2=4;  y=2.5=10

đặt x/3=y/8=z/5=k

=> x=3k

     y=8k

      z=5k

mà 3x+y-2z=35

<=> 3(3k)+8k-2(5k)=35

<=> 9k+8k-10k=35

<=>k(9+8-10)=35

<=>k8=35

k=35/8

sau đó bạn tự thay vào nhé

Ta có : \(\frac{x}{5}\)= \(\frac{y}{7}\)= \(\frac{z}{8}\)= \(\frac{x+y+z}{5+7+8}\)= \(\frac{18}{20}\)= \(\frac{9}{10}\)

Vậy : x = 5 .\(\frac{9}{10}\)= 4,5

y = 7 . \(\frac{9}{10}\)= 6,3

Chúc bạn học tốt !

z = 8. \(\frac{9}{10}\)= 7,2