Áp dụng t/c dãy tỉ số bằng nhau:

a.

\(\dfrac{x}{2}=\dfrac{y}{5}=\dfrac{x+y}{2+5}=\dfrac{-21}{7}=-3\)

\(\Rightarrow\left\{{}\begin{matrix}x=2.\left(-3\right)=-6\\y=5.\left(-3\right)=-15\end{matrix}\right.\)

b.

\(5x=3y\Rightarrow\dfrac{x}{3}=\dfrac{y}{5}=\dfrac{x-y}{3-5}=\dfrac{10}{-2}=-5\)

\(\Rightarrow\left\{{}\begin{matrix}x=3.\left(-5\right)=-15\\y=5.\left(-5\right)=-25\end{matrix}\right.\)

c.

\(\dfrac{x}{5}=\dfrac{y}{2}=\dfrac{3x}{15}=\dfrac{-2y}{-4}=\dfrac{3x-2y}{15-4}=\dfrac{44}{11}=4\)

\(\Rightarrow\left\{{}\begin{matrix}x=5.4=20\\y=2.4=8\end{matrix}\right.\)

d.

\(\dfrac{x}{3}=\dfrac{y}{16}=\dfrac{3x}{9}=\dfrac{-y}{-16}=\dfrac{3x-y}{9-16}=\dfrac{35}{-7}=-5\)

\(\Rightarrow\left\{{}\begin{matrix}x=3.\left(-5\right)=-15\\y=16.\left(-5\right)=-80\end{matrix}\right.\)

\(\dfrac{18}{21}=\dfrac{6}{7}\)=\(\dfrac{12}{14}=\dfrac{36}{42}\)=\(\dfrac{90}{150}=\dfrac{3}{5}\)=\(\dfrac{12}{20}=\dfrac{60}{100}=\dfrac{21}{35}\)

\(\dfrac{18}{21}=\dfrac{12}{14}=\dfrac{6}{7}=\dfrac{36}{42}\)

\(\dfrac{90}{150}=\dfrac{12}{20}=\dfrac{60}{100}=\dfrac{3}{5}=\dfrac{21}{35}\)

giúp mình với, đi mà

Tìm x biết : /2x-1/=3 

Th1 : | 2x - 1 | = 3

           2x = 4 

x = 2 

Th2 :  : /2x-1/=-3

             2x - 1 = -2 

x  = -1 

k nha

a) x=4 và x=-1

b) \(\frac{16}{25}\)

1) /2x-1/ tương đương 2x-1=3 hoặc -3

th1) 2x-1=3

suy ra 2x=4

x=2

th2) 2x-1=-3

suy ra 2x=-2

x=-1 

2) (4/5)​^5 \(\times\)x= (4/5)^7

\(\Leftrightarrow\)x = (4/5)^7 \(\div\)(4/5)^5

\(\Leftrightarrow\)x=(4/5)^2=16/25

bài 1

a, X/Y x 1/5=3/10

X/Y=3/10:1/5

X/Y=3/2

b, 3/4 x X/Y= 6/5

X/Y=3/4:6/5

X/Y=5/8

Bài 2:

a, >     b, <       c,=        d,<

a, (x-15):5+22=24

    ( x - 15 ) : 5 = 2

      x-15  = 10

       x = 25

1)4+x=7

=>x=7-4=3

2)2x+(-5)=-18

=>2x=-18-(-5)=-18+5=-13

=>x=-13:2=-13/2

=>x thuộc rỗng

(-14)+x-7=10

=>(-14)+x=10+7=17

a  tìm số nguyên x biết (x-5).(y-7)=1 
   (x-5).(y-7)=1 = 1.1 = -1.(-1) 
   TH1,
   x-5 = 1, y-7 = 1
   => x = 6, y = 8
   TH2