# Basic algebra concept is puzzling me

1. Dec 22, 2011

### TheKracken

basic algebra concept is puzzling me....

1. The problem statement, all variables and given/known data
I don't understand why √10-5 + √5 = 2√5
Could someone please explain this to me real quick...totaly forgot why this is :P

2. Relevant equations
none

3. The attempt at a solution
here I am! thoughts about it and I am still puzzled does it have anything to do with the fact that √10-5 =√5 and then we add another √5 to it and there is some rule that says that you take one of them away and just put a 2 infront of √5 and it is equivilant?

2. Dec 22, 2011

### Dick

Re: basic algebra concept is puzzling me....

Yes. sqrt(5)+sqrt(5)=2*sqrt(5). Is that really something you forget? It's kind of the definition of multiplication.

3. Dec 22, 2011

### TheKracken

Re: basic algebra concept is puzzling me....

its probobly just all the √ and stuff...it often scares me and I think automaticaly different rules apply or something....

could someone explain limit equations with trig functions in them? I have no idea how to figure these out....for example:
limit as x->0 for x/sin3x

Last edited by a moderator: Dec 23, 2011
4. Dec 22, 2011

### Dick

Re: basic algebra concept is puzzling me....

No, no different rules apply. For the second one, do you know limit as u->0 u/sin(u)=1? If so, put u=3x.

Last edited by a moderator: Dec 23, 2011
5. Dec 22, 2011

### TheKracken

Re: basic algebra concept is puzzling me....

so the answer would be 1/3 yes?
now if it was instead sin 5x would it now be 1/5?
thank you for help!

Last edited by a moderator: Dec 23, 2011
6. Dec 23, 2011

### checkitagain

Re: basic algebra concept is puzzling me....

TheKracken,

you must use grouping symbols around this radicand, otherwise what
you have is

√(10) - 5 + √5 = 2√5, which is not what you meant.

7. Dec 23, 2011

### Dick

Re: basic algebra concept is puzzling me....

You're welcome. Sure. The answer is 1/3.

Last edited by a moderator: Dec 23, 2011