Solving Inequalities: How Do I Determine the Correct Answer?

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So, if you consider the following cases:1. Both terms are negative, and the result is positive, which doesn't satisfy the inequality.2. Both terms are positive, and the result is positive, which satisfies the inequality.3. Both terms are negative, and the result is negative, which satisfies the inequality.4. Both terms are positive, and the result is negative, which doesn't satisfy the inequality.So, we can see that the inequality is satisfied when both terms are negative or both are positive. This can be written as (-)(-) or (+)(+) for the case of (x-4) and (x), respectively. Therefore, the solution is x<0 or x>4.In summary, when
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How would I solve the inequality (X-4)/X>0. I thought that inequalities were solved in the same way equations were, but when I solve that way I get X>4 which isn't the entire answer.
 
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For this one, it is best to look at critical points where either the top or bottom equal zero. From that, you should be able to quickly categorize the intervals where the expression is true.
 
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Scheuerf said:
How would I solve the inequality (X-4)/X>0. I thought that inequalities were solved in the same way equations were
No, they're not. For example, if you multiply both sides of an equation by, say, -1, you get a new equation that is equivalent to the one you started with.

If you multiply an inequality by -1, the inequality symbol changes direction.
Scheuerf said:
, but when I solve that way I get X>4 which isn't the entire answer.
 
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Well, what you do is:
x-4: Negative when x<4, positive when x>4
x: Negative when x<0, positive when x>0
Expression: Positive when x<0 (neg. and neg. makes pos.), negative when 0<x<4 and positive when x>4
 
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  • #5
Svein said:
Well, what you do is:
x-4: Negative when x<4, positive when x>4
x: Negative when x<0, positive when x>0
Expression: Positive when x<0 (neg. and neg. makes pos.), negative when 0<x<4 and positive when x>4
Or, more simply, just multiply both sides of the inequality by x2, first making a note that x cannot be zero. For x ≠ 0, x2 > 0, so the direction of the inequality doesn't change.
 
  • #6
When I solve that way I get x>0 and x>4. Am I doing something wrong?
 
  • #7
The correct answer was given in post 4.
##\frac{x-4}{x} >0 ##
Taking Mark44's recommendation, this could also be seen as:
##x^2\frac{x-4}{x} >0*x^2 ##
##x(x-4) >0##
Remember that (-)(-)=(+) and (+)(+)=(+), and (-)(+)=(-) just the same as (-)/(-)=(+) and (+)/(+)=(+), and (-)/(+)=(-).
So whether or not you multiply by ##x^2##, you still need to find the signs of your terms (x-4) and (x) and the appropriate regions.
Build a simple table, the inequality will only hold true if both terms are negative or both are positive.
 
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FAQ: Solving Inequalities: How Do I Determine the Correct Answer?

What is a simple inequality?

A simple inequality is a mathematical statement that compares two quantities using symbols such as <, >, ≤, or ≥. It states that one quantity is greater than or less than another quantity.

How do you graph a simple inequality?

To graph a simple inequality, first rewrite it in slope-intercept form (y = mx + b). Then, plot the y-intercept (b) on the y-axis and use the slope (m) to find a second point on the line. Finally, shade the area above or below the line depending on the inequality symbol.

What is the solution set of a simple inequality?

The solution set of a simple inequality is the set of all values that make the inequality true. It can be represented by a graph or written in interval notation.

How does solving a simple inequality differ from solving an equation?

Solving a simple inequality is similar to solving an equation, but there are a few key differences. When solving an inequality, the solution may be a range of values rather than a single value. Also, when multiplying or dividing both sides of an inequality by a negative number, the direction of the inequality symbol must be reversed.

What is the difference between a strict and non-strict inequality?

A strict inequality uses the symbols < and > and indicates that the two quantities are not equal to each other. A non-strict inequality uses the symbols ≤ and ≥ and indicates that the two quantities can be equal to each other.

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