Solving inequalities (need some clarification)

It's impossible for a number to be simultaneously greater than 4 and less than 2. Therefore, there are no solutions for this inequality.
  • #1
Nitrate
75
0

Homework Statement



Solve x/(x-2) > 2 by first rewriting it in the form P(x)/Q(x)>0

Homework Equations





The Attempt at a Solution


well... i got up to
x/(x - 2) > 2
x/(x - 2) - 2 > 0
x/(x - 2) - 2(x - 2)/(x - 2) > 0
x/(x - 2) - (2x - 4)/(x - 2) > 0
(x - 2x + 4)/(x - 2) > 0
(-x + 4)/(x - 2) > 0
-x + 4 > 0 and x - 2 > 0 OR -x + 4 < 0 and x - 2 < 0

However, i do not understand why there has to be an OR case if the inequality is only >

please help :)
 
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  • #2
Nitrate said:

Homework Statement



Solve x/(x-2) > 2 by first rewriting it in the form P(x)/Q(x)>0

Homework Equations





The Attempt at a Solution


well... i got up to
x/(x - 2) > 2
x/(x - 2) - 2 > 0
x/(x - 2) - 2(x - 2)/(x - 2) > 0
x/(x - 2) - (2x - 4)/(x - 2) > 0
(x - 2x + 4)/(x - 2) > 0
(-x + 4)/(x - 2) > 0
-x + 4 > 0 and x - 2 > 0 OR -x + 4 < 0 and x - 2 < 0

However, i do not understand why there has to be an OR case if the inequality is only >

please help :)

Because numerator and denominator are either both positive OR both negative.
 
  • #3
Mark44 said:
Because numerator and denominator are either both positive OR both negative.

the rationale being that a (+/+) = + and (-/-) = +
right?
 
  • #4
okay another question
why would we do the following (the part with ***), what does it mean by no solutions: x/(x - 2) > 2
x/(x - 2) - 2 > 0
x/(x - 2) - 2(x - 2)/(x - 2) > 0
x/(x - 2) - (2x - 4)/(x - 2) > 0
(x - 2x + 4)/(x - 2) > 0
(-x + 4)/(x - 2) > 0
-x + 4 > 0 and x - 2 > 0 OR -x + 4 < 0 and x - 2 < 0
x < 4 and x > 2 OR x > 4 and x < 2
*****x > 4 and x < 2 has no solutions so discard it, leaving just
 
  • #5
Because there aren't any numbers that satisfy x > 4 and x < 2.
 

Related to Solving inequalities (need some clarification)

1. What is an inequality?

An inequality is a mathematical statement that compares two quantities or expressions and shows their relative sizes. It uses symbols such as <, >, ≤, and ≥ to represent the relationship between the two quantities.

2. How do you solve an inequality?

To solve an inequality, you need to isolate the variable on one side of the inequality sign. This can be done by using inverse operations, similar to solving an equation. However, when multiplying or dividing both sides by a negative number, the inequality sign must be flipped.

3. Can you graph inequalities?

Yes, inequalities can be graphed on a number line or a coordinate plane. The solution to an inequality is represented by a shaded region on the graph, depending on the type of inequality and whether the solution includes or excludes certain values.

4. What is the difference between a linear and quadratic inequality?

A linear inequality contains a variable raised to the first power, while a quadratic inequality contains a variable raised to the second power. This means that the graph of a linear inequality is a straight line, while the graph of a quadratic inequality is a curve.

5. Are there any special rules for solving compound inequalities?

Yes, compound inequalities are inequalities that contain more than one inequality statement. When solving these, it is important to consider the relationship between the two inequalities and use the correct combination of solutions. For example, if the two inequalities are joined by "and", the solution must satisfy both inequalities, while if they are joined by "or", the solution can satisfy either one of the inequalities.

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