+0  
 
+5
917
11
avatar

what is square root of (-8)^2 ?

 Jul 13, 2016

Best Answer 

 #4
avatar+33666 
+10

WolframAlpha, Matlab, Mathcad and Maple all give the following:

 

root

.

 Jul 13, 2016
 #1
avatar
+5

\({({(-8)^2})^{1\over2}}={(-8)^{1}}=-8\)

 

I would say that since \({(-8)^2}={8^2}\)

8 is also a solution.

 Jul 13, 2016
 #2
avatar+118725 
+5

what is square root of (-8)^2 ?

 

\((-8)^2=64\\ \sqrt{64}=+8\)

 

 

+8 IS THE ONLY SOLUTION

 Jul 13, 2016
edited by Melody  Jul 13, 2016
 #3
avatar+118725 
+5

You do make a very interesting point answering guest.

 

\(\sqrt{(-8)^2}=\sqrt{64}=+8\\ BUT\\ \mbox{If you use index laws then}\\ \sqrt{(-8)^2}= ((-8)^2)^{0.5} =(-8)^{2*0.5}=(-8)^1=-8 \)

 

I still think the answer is +8 but I would like other mathematicians to comment on this.    frown

 Jul 13, 2016
 #4
avatar+33666 
+10
Best Answer

WolframAlpha, Matlab, Mathcad and Maple all give the following:

 

root

.

Alan Jul 13, 2016
 #5
avatar+33666 
+5

The last of the above ignores a set of parentheses (implied in the way the original question is specified), hence does not comply with PEDMAS.  So I'm with Melody on the solution.

Alan  Jul 13, 2016
 #6
avatar+67 
+5

I am with Melody too

MichaelShaun  Jul 13, 2016
 #7
avatar+118725 
+1

It is interesting when these types of contradictions spring up :)

 

Thanks Alan and Michael  :)

 Jul 13, 2016
 #8
avatar
+5

I see I sparked some discussion. So the difference is in paying close attention as to exactly how you formulate the problem.

Thanks all.

 Jul 13, 2016
 #9
avatar+67 
0

Exactly

MichaelShaun  Jul 13, 2016
 #10
avatar+130561 
0

Here's another way to consider this :

 

l a l   =  √(a^2)       

 

If we let a = -8, we have

 

l a l   = l -8 l  =   √ [ (-8)^2 ]   = √ [64]   =   8  

 

 

cool cool cool 

 Jul 13, 2016

1 Online Users