Question

Tìm x biết

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

\(\frac{7}{x-1}=\frac{x+1}{9}\)

Answer 1

a) x= 23

b) x=8

Answer 2

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

=> 7 ( x - 3 ) = 5 ( x + 5 )

7x - 21 = 5x + 25

7x - 5x = 25 + 21

2x = 46

x = 23

Answer 3

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

=>   \(7\left(x-3\right)=5\left(x+5\right)\)

<=>  \(7x-21=5x+25\)

<=>  \(2x=46\)

<=>  \(x=23\)

Vậy...

\(\frac{7}{x-1}=\frac{x+1}{9}\)

<=>  \(\left(x-1\right)\left(x+1\right)=63\)

<=>  \(x^2-1=63\)

<=>  \(x^2=64\)

<=>  \(x=\pm8\)

Vậy...

Answer 4

a, (=) (x-3).7=5.(x+5)

(=)7x-21=5x+25

(=)7x-5x=25+21

(=)2x=46

(=)x=23

b,(=)(x-1)(x+1)=63

mà 63=1.63=7.9

mà (x-1)(x+1) là 2 số tự nhiên cách nhau 2 đơn vị

=>\(\orbr{\begin{cases}x-1=7\\x+1=9\end{cases}\left(=\right)\orbr{\begin{cases}x=8\\x=8\end{cases}}}\)

=>x=8

Answer 5

Tìm x , biết : 

x - 3 / x + 5 = 5/7 

<=> ( x - 3 ) . 7 = ( x + 5 ) . 5 

<=> 7x - 21 = 5x + 25 

<=> 7x - 5x = 25 + 21 

<=> 2x = 46 

<=> x = 46 : 2 

<=> x = 23

Vậy x = 23 

7 / x - 1 = x + 1 / 9 

<=> ( x - 1 ) . ( x + 1 ) = 7 . 9

<=> x . ( x + 1 ) - 1 . ( x + 1 ) = 63

<=> x ² + x - x - 1 = 63 

<=> x² + 0 - 1 = 63 

<=> x²  + 0 = 63 + 1 

<=> x² + 0 = 64 

<=> x² = 64 - 0 

<=> x² = 64 

<=> x² = 8² hoặc (-8)²

=> x = 8 hoặc -8

Vậy x € { 8 ; -8 }