Ta suy ra:

x+3/y+5 = x+5/y+7  = (x+3-x-5)/(y+5-y-7) = -2/-2 =1

x+3 /y+5 =1 => x+3 =y+5

                   => x-y = 5-3 =2

Vay x-y =2

Ap dung tinh chat day ti so bang nhau : 

x+3/y+5=x+5/y+7=(x+5)-(x+3)/(y+7)-(y+5)=x+5-x-3/y+7-y-5=2/2=1

Suy ra : x+3/y+5=1=>x+3=y/5

=>x-y=5-3=2

Vay x-y=2

**** nhe

\(\frac{x+3}{y+5}=\frac{x+5}{y+7}=\frac{x+5-x-3}{y+7-y-5}=\frac{2}{2}=1\)

\(x+3=y+5\Leftrightarrow x-y=5-3=2\)

Ap dung tinh chat day ti so bang nhau : 

\(\frac{x+3}{y+5}=\frac{x+5}{y+7}\Rightarrow\left(x+3\right)\left(y+7\right)=\left(y+5\right)\left(x+5\right)\)

                         \(\Rightarrow xy+7x+3y+21=xy+5x+5y+25\)

                         \(\Rightarrow7x+3y=5x+5y+25-21\)

                               \(7x-5x=5y-3y+4\)

                                          \(2x=2y+4\Rightarrow2x-2y=4\)

                              \(2\left(x-y\right)=4\Rightarrow x-y=4:2=2\)

                                  Vay :x-y=2

**** nhe

(x+3)/(y+5)=(x+5)/(y+7)

(x+3)(y+7)=(y+5)(x+5)

x(y+7)+3(y+7)=y(x+5)+5(x+5)

xy+7x+3y+21=xy+5y+5x+25

7x+3y+21=5y+5x+25

(7x-5x)-(5y-3y)=25-21

2x-2y=4

2(x-y)=4

x-y=4/2

x-y=2

vừa dễ mà vừa khó

hay thì tích nha

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

\(\frac{x+3}{y+5}=\frac{x+5}{y+7}=\frac{\left(x+3\right)-\left(x+5\right)}{\left(y-5\right)-\left(y+7\right)}=\frac{x+3-x+5}{y+5-y+7}=\frac{3-5}{5-7}=\frac{-2}{-2}=1\)

\(\Rightarrow\frac{x+3}{y+5}=\frac{x+5}{y+7}=1\)

\(\Rightarrow\left(x+3\right).1=\left(y+5\right).1\)

\(\Rightarrow x+3=y+5\)

\(\Rightarrow x-y=5-3\)

\(\Rightarrow x-y=2\)

Vậy x - y = 2.

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