+0  
 
0
1068
3
avatar+980 

Why does the sign flip?

 

k² > 68

k > √68   and k < -√68

 

I understand it's true and you can see it by graphing but is there a rule? Like "when you take the negative root of something the sign flips"?

 May 25, 2015

Best Answer 

 #1
avatar+118587 
+15

Just think about it logically Zac,  I'll use a simpler example

$$k^2>25$$

 If k=6 then k^2=36 so this makes the statement true

If k=-6 then x^2=36 so this makes the statement true too.

For any value of k between -5 and +5 the statement will be false.

So it will be true when

k>5   and when  k<-5

 

It may help you understand if you draw a number line.  I often think of number lines when I answer inequalities.

 

Have I answered your question or were you hoping for something different ?

 May 25, 2015
 #1
avatar+118587 
+15
Best Answer

Just think about it logically Zac,  I'll use a simpler example

$$k^2>25$$

 If k=6 then k^2=36 so this makes the statement true

If k=-6 then x^2=36 so this makes the statement true too.

For any value of k between -5 and +5 the statement will be false.

So it will be true when

k>5   and when  k<-5

 

It may help you understand if you draw a number line.  I often think of number lines when I answer inequalities.

 

Have I answered your question or were you hoping for something different ?

Melody May 25, 2015
 #2
avatar+980 
+5

Thanks, I think I understand. The surds might have been throwing me off. 

 May 25, 2015
 #3
avatar+118587 
+5

Yes whenever there is a complication in a question that gets in the way of grasping the technique needed, always get rid of it and look at an similar example with kinder numbers or letters.

I still do this quite regularly    

 May 25, 2015

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