Which of the following is NOT a surd ?

CPhill, that sounds absurdly irrational!

I hope you can hear this. 

C is not a surd.

sqrt(9+7) = sqrt(16) = 4

The rest are decimals since they cannot be simplified to remove the sqrt symbol.

sqrt(9) by itself is not a surd, but with the + / - sqrt(7) [which cannot be simplified like sqrt(4), sqrt(25), etc.] it is a surd.

I've not run across the term "surd" before......Simply put, it is a number that cannot be simpified to remove a root (an irrational number is the result).....

How did we get the word "Surd" ?

Well around 820 AD al-Khwarizmi (the Persian guy who we get the name "Algorithm" from) called irrational numbers "'inaudible" ... this was later translated to the Latin surdus ("deaf" or "mute")

BTW......Thanks Aziz, for that answer........

I can - All smiles from me.