+0  
 
+2
505
4
avatar+7399 

Where is written:

\( \sqrt {4} = 2 \\ \sqrt {4} \neq-2\) 

 

smiley  ?

asinus  Sep 29, 2017
 #1
avatar+17743 
+3

There are two square roots of 4:  2  and  -2.

The positive square root is called the "principal root".

The square root sign is defined to mean the principal root; thus, sqrt(4) = 2, not -2.

geno3141  Sep 30, 2017
 #2
avatar+7399 
0

Where is written?

Thank you Geno,
but is there somewhere to read?

laugh  ?

asinus  Sep 30, 2017
 #3
avatar+26839 
+1

Try:  http://mathworld.wolfram.com/PrincipalSquareRoot.html 

Alan  Sep 30, 2017
 #4
avatar+7399 
+1

Thank you Alan!

Everything is clear now.

laugh  !

asinus  Sep 30, 2017

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