Posted by Tammie on Saturday, July 25, 2009 at 9:45pm.
Just wondering if I did this correctly step by step. If not corrections are mostly appreciated!
Solve the inequality and write the solution set in interval notation. Show work/explanation.
(x+8)/(x-1) >= 0
x-1/9 < -1
x+8/x> = 1
x^2+8> = x
8 > -1
x < -8 OR x>1
(-‡,-8] ¾ (1, ‡)
Is this all of what I need to show for how I got my answer?
Algebra - Reiny, Saturday, July 25, 2009 at 10:10pm
There are several ways to do this.
Your way is the oddest way I have ever seen. It looks like you are actually doing a long division to get
(8+x)/(x-1)=1+9/(x-1) (notice my brackets to make your statement from above actually true.)
Here is a logical way:
since the answer to the fraction is positive, either both top and bottom are positive or they are both negative.
[x+8≥0 and x-1>0] OR [x+8≤0 and x-1≤0]
[x≥-8 and x>1] OR [x≤-8 and x≤1]
x > 1 or x ≤ -8
so you did get the right answer.
The way I do these is this :
From the factored form, I can see two "critical values" namely -8 and 1
So my number line is split into 3 sections:
a) x ≤ -8
b) between -8 and 1
c) x >1
I then pick an arbitrary number in each region. We don't actually have to evaluate, just get the sign correctly.
a) let x=-10, then -/- >0 , which works
b) let x=0, then +/- < 0 , does not work
c) let x=10 then +/+ > 0 , works
so x ≤ -8 or x > 1
Algebra - Tammie, Saturday, July 25, 2009 at 10:28pm
Thank you for the review on this topic!
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