Solve inequality by factoring help

In summary, the inequality x^2 + 8x + 15 > 0 can be solved by first factoring the expression into (x+5)(x+3)>0. Then, you can find two possible solutions: x+5>0 ; x>-5 and x+3>0 ; x>-3. These can be combined to get the final solution of (-\propto, -5) \cup (-3, +\propto). However, this method is time-consuming and there is a much easier way to solve the inequality.
  • #1
DeanBH
82
0
x^2 + 8x + 15 > 0 solve inequality

(X+5)(X+3)>0


x+5>0 x>-5
X+3>0 x>-3

Why is the equality for X+5>0 x<-5 ? as the answers give?
 
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  • #2
Because you have two possible solutions for (x+5)(x+3)>0

the first one:

x+5>0 ; x>-5

x+3>0 ; x>-3

[tex](-5, +\propto) \cap (-3, +\propto) = (-3, +\propto)[/tex]

and the second

x+5<0 ; x<-5

x+3<0 ; x<-3

[tex](-\propto, -5) \cap (-\propto, -3) = (-\propto, -5) [/tex]

The final solution:

[tex](-\propto, -5) \cup (-3, +\propto)[/tex]

Anyway, this way is much more time-consuming... So you shouldn't use it in future.. There is much easier way...
 
  • #3
Physicsissuef said:
Because you have two possible solutions for (x+5)(x+3)>0

the first one:

x+5>0 ; x>-5

x+3>0 ; x>-3

[tex](-5, +\propto) \cap (-3, +\propto) = (-3, +\propto)[/tex]

and the second

x+5<0 ; x<-5

x+3<0 ; x<-3

[tex](-\propto, -5) \cap (-\propto, -3) = (-\propto, -5) [/tex]

The final solution:

[tex](-\propto, -5) \cup (-3, +\propto)[/tex]

Anyway, this way is much more time-consuming... So you shouldn't use it in future.. There is much easier way...

you could have just said

"because if X > -5 then the first bracket will become negative and then (x+5)(x+3) wouldn't be > 0."


but ok. =P

btw : i just realized why
 

What is an inequality?

An inequality is a mathematical statement that compares two quantities using symbols such as <, >, ≤, or ≥. It shows that one quantity is greater or less than the other.

Why do we need to solve inequalities by factoring?

Solving inequalities by factoring allows us to find the values or range of values that make the inequality true. This is especially useful when working with equations that involve variables or unknown values.

What is factoring?

Factoring is the process of breaking down a polynomial or algebraic expression into smaller parts that can be easily multiplied to obtain the original expression. In the context of inequalities, factoring helps us find the values that satisfy the inequality by simplifying the expression.

How do you solve an inequality by factoring?

To solve an inequality by factoring, first set the expression equal to 0. Then, factor the expression into smaller parts. Next, use the Zero Product Property to find the values that make each factor equal to 0. Finally, use a number line to plot the solutions and determine the final solution set.

Can you provide an example of solving an inequality by factoring?

Yes, for example, to solve the inequality x^2 + 3x - 10 > 0, we first set it equal to 0: x^2 + 3x - 10 = 0. Then, we factor the expression into (x+5)(x-2) = 0. Using the Zero Product Property, we find that x = -5 or x = 2. We plot these values on a number line and see that the solution set is x < -5 or x > 2. Therefore, the inequality is true when x is either less than -5 or greater than 2.

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