What is the square root of 6 ?

It's an irrational number ... it can never be written down on paper exactly.

The beginning of it is  2.449489...  and it keeps going forever.

You might think that using only part of a number in a problem makes your
answer wrong.  In a way that's true.  But if you use 2.449489 for the square-
root of 6, then your final answer is only about  0.00003  percent wrong, and
that's close enough ... even if you're building bridges or spacecraft.

"But", you say, "How can I hand in an answer on my homework that's wrong ?"

Here's a secret that's so big that nobody ever talks about it. Once you know it,
it'll change your whole way of thinking.  And you'll stop fishing for answers on
the internet:

The answers in homework don't matter !   The answer is the least important
part of any homework problem, and nobody needs it.  If your teacher needed
an answer, then he/she could get it a lot faster by working out the problem. 
If he/she didn't have time to work on it, then the teacher would go to somebody
who knows it cold ... they certainly wouldn't ask somebody who's just learning
it for the first time.

The purpose of the homework is NOT to generate answers.  It's to lead you
down the path of learning how to do the problem.  When somebody else gives
you the answer and you hand it in, 2 things happen: 

#1: you cheat;
#2: you don't learn anything.

It's a bad deal all around.

2.) is the most sense