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Find all x such that 4<1x<3.

 Feb 14, 2022
 #1
avatar+364 
+1

ok..

i don't know if this is possible..

x can equal 1 to infinity and it works

 Feb 15, 2022
 #2
avatar+2668 
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Note that 113 is 3. When x gets bigger, the value of the expression gets smaller. 

 

Likewise, 114 is -4. As x gets smaller than 14, the value of the equation gets bigger, but never is greater than 0. 


So, the 2 ranges that work are x<14 and x>13

BuilderBoi  Feb 15, 2022
edited by BuilderBoi  Feb 15, 2022
 #3
avatar+23254 
+1

Rewrite  -4  <  1/x  < 3  into its two parts:  -4  <  1/x   and   1/x  <  3

 

Divide the problem into two parts:

Part 1:  x < 0:

            (Remember that when you multiply both sides of an inequality by a negative number,

              you must change the sense of the inequality.

              Also remember that, for this part, x is negative.)

 

            -4 < 1/x   --->   -4x > 1   --->   x < -1/4

            1/x < 3   --->   1 > 3x   --->   3x < 1   --->   x < 1/3

 

            Since these two inequalities are combined by the word and, the solution to this

            part is the more restrictive of the two answers:  x < -1/4    

 

Part 2:  x > 0

 

             -4 < 1/x   --->   -4x < 1   --->   x > -1/4

             1/x < 3   --->   1 < 3x   --->   3x > 1   --->   x > 1/3

 

             The more restrictive of these two is:  x > 1/3

 

Since the answer consists of two parts, either Part 1 or Part 2, the final answer is the 

     region:  x < -1/4  or  x > 1/3

     which is:  (-inf, -1/4)  union  (1/3, inf)

 Feb 15, 2022

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