Math question (algebra)

[SarcasticDwarf]

How is it that the following queation's answer is a negative infinity (a - followed by a rotated 8)?

-9x + 3x (greater than or equal to sign) - 24

Which comes to: (-infinity, 4]



thanks

 

[demenion]

-9x + 3x = -6x

divide both sides by -6

-6x/-6 = -24/-6

x = 4

flip sign because divided by a negative.

x less than or equal to 4

 

[notfred]

because anything between -infinity and 4, when put into -9x+3x is greater than or equal to 24.

 

[Legendary]

-6x >= -24
x <= 4
(-infinity, 4] means all real numbers from negative infinity (which can never have a [ next to it, only a ( because it cannot be included in a solution set) all the way to 4, inclusive
() means exclusive
[] means inclusive

 

[SarcasticDwarf]

Originally posted by: Legendary
-6x >= -24
x <= 4
(-infinity, 4] means all real numbers from negative infinity (which can never have a [ next to it, only a ( because it cannot be included in a solution set) all the way to 4, inclusive
() means exclusive
[] means inclusive

But why does one problem have a negative infinity while others have a positive infinity? Are the positive infinities only in cases where the equation comes to x is greater than 0?

 

[marketsons1985]

with negative infinity, when you multiply the -9 by it, it becomes a whomping big ass number, so it's greater than 24, if it was positive infinity, it'd be a negative that was 9 times the other one, making it negative.