Some really basic maths help

divine` · 6 Dec 2007 at 18:58

My mind has gone totally blank and all my GCSE/ALevels notes are a mess and I can't find what im looking for online as i'm not sure what the process is called.

Anyway

Say I have √15

I want to simplify it a bit. I remember from A Level there is a way of moving 'some' of it outside the root and creating a number like 3√13 etc.

How do I actually do this though? I would like to get a 2 outside as it would simplify the rest of the work a fair amount if I could.

I thought 2√11 might be it but I don't think it is :/

Any help?

thenormalman · 6 Dec 2007 at 19:00

with square roots, you can change them to two factors which multiplied by each other would make the square.

e.g. √24 would be equal to √4 x √6
You can then simplify this to 2√6 (because 2 is √4)

Ben M · 6 Dec 2007 at 19:00

ugh sorry

divine` · 6 Dec 2007 at 19:01

ah i see, so i'm not really going to be simplify it to anything useful then

cuppy tea · 6 Dec 2007 at 19:02

neodude · 6 Dec 2007 at 19:02

√15 Can't be simplified any further.

gumbald · 6 Dec 2007 at 19:03

Ben M said:
√7√8

7 x 8 =/= 15

Ben M · 6 Dec 2007 at 19:03

gumbald said:
7 x 8 =/= 15

thought you added them -.-

thenormalman · 6 Dec 2007 at 19:03

Ben M said:
√15 is √3√5 or √7√8

iirc

Nope... √7√8 would be √56... you multiply them - not add them

gumbald · 6 Dec 2007 at 19:05

Ben M said:
thought you added them -.-

You managed the 3 x 5 in the same post

richard104 · 6 Dec 2007 at 19:05

they are called surds arent they?

Tefal · 6 Dec 2007 at 19:05

cuppy tea said:
42

hehehe True, once yelled that at a teacher after being woken up in class

...it was an english lesson

And now its my room number at uni, and the code for the only decent drink in the snack machine Apple juice

It truly is the answer.

gumbald · 6 Dec 2007 at 19:07

richard104 said:
they are called surds arent they?

Always makes me chuckle because of a teacher that used to say it strangely.

jaykay · 6 Dec 2007 at 19:07

15 cant be simplified. There's no root number that goes into it.

divine` · 6 Dec 2007 at 19:07

Basically I need to solve the quadratic m+m+4=0

Which unless I am mistaken leaves me with the roots as

(-1+√-15)/2 and (-1-√-15)/2

which i've then made

(-1+√15i)/2 and (-1-√15i)/2

However I then need to use those for the rest of my problem (solving a differential equation) so having them like that is a slight pain :/

yhack · 6 Dec 2007 at 19:08

neoduder said:
√15 Can't be simplified any further.

3√5 surely?
Unless I have forgotten how to do surds in a week. I was doing it at school last week.

richard104 · 6 Dec 2007 at 19:10

yhack said:
3√5 surely?
Unless I have forgotten how to do surds in a week. I was doing it at school last week.

no you can only take 3 out if its multiplied by 9 e.g

√18=3√2

yhack · 6 Dec 2007 at 19:11

richard104 said:
no you can only take 3 out if its multiplied by 9 e.g

√18=3√2

Ah yeah ok.
I'm silly.

richard104 · 6 Dec 2007 at 19:14

i think you have go the right answer divine, as you cant simplfy anymore. i will check though

[TR]SweetSpotOz · 6 Dec 2007 at 20:55

divine` said:
Basically I need to solve the quadratic m+m+4=0

Which unless I am mistaken leaves me with the roots as

(-1+√-15)/2 and (-1-√-15)/2

which i've then made

(-1+√15i)/2 and (-1-√15i)/2

However I then need to use those for the rest of my problem (solving a differential equation) so having them like that is a slight pain :/

What is the next part of the question?