SOLUTION: 0<(9x-27)^-1<1/9

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Question 898933: 0<(9x-27)^-1<1/9
Found 2 solutions by CubeyThePenguin, ikleyn:
Answer by CubeyThePenguin(3113) About Me  (Show Source):
You can put this solution on YOUR website!
0 < 1/(9x-27) < 1/9
0 < 9x - 27 < 9
27 < 9x < 36

3 < x < 4

Answer by ikleyn(52790) About Me  (Show Source):
You can put this solution on YOUR website!
.

            The solution by  @CubeyThePenguin is  INCORRECT.

            I came to bring you a correct solution.


You start from this inequality


    0 < (9x-27)^(-1) < 1/9


It is equivalent to the system of two inequalities


    0 < (9x-27)^(-1)          (1)
and
        (9x-27)^(-1) < 1/9    (2)


connected with the service word "and".


First inequality (1)  is  0 < 1%2F%289x-27%29;  it is equivalent to  9x - 27 > 0;  x - 3 > 0  and finally  x > 3.


        So for what is follows, we can assume x > 3.     (3)


Second inequality (2)  is  1%2F%289x-27%29 < 1/9;  it is equivalent to  1%2F%28x-3%29 < 1  and finally 

(taking into account that x > 3) it implies  1 < x-3; hence x > 4.   (4)


Thus we get the final answer  x > 4.


ANSWER.  The solution set is  x > 4.


                         Visual CHECK



       


      Figure.  Plot y = 1%2F%289x-27%29 (red)  and y = 1%2F9 (green)

Solved  (correctly).