Question

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

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

Answer 1

a) Ta có: x - 3/x + 5 = 5/7

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

                7x - 21 = 5x + 25

                 7x - 5x = 21 + 25

                     2x    = 46

                       x    = 46 : 2

            Vậy    x = 23

b) 7/x - 1 = x + 1/9

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

 => x = 7.

Answer 2

7x-21=5x+25

7x-5x=46

2x=46

x=23

Answer 3

x²-1=63

x²=64

x=8 hoặc x=-8

Answer 4

Xin lỗi, câu b mình nhầm:

b) 7/x - 1 = x + 1/9

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

=> 63    = [(x + 1) . x] - [(x + 1) . 1]

=> 63    = [x^2 + x] - [x + 1]

=> 63    = x^2 + x - x - 1

=> 63    = x^2 - 1

=> 64    = x^2

Vậy x = 8 hoặc x = -8.