# surd help urgent

• Mar 16th 2007, 07:29 PM
mini
surd help urgent
the question states "write an irrational fraction that when rationalised the solution is 5. prove":confused: :eek:

your help would be much appreciated
• Mar 17th 2007, 02:41 AM
CaptainBlack
Quote:

Originally Posted by mini
the question states "write an irrational fraction that when rationalised the solution is 5. prove":confused: :eek:

your help would be much appreciated

Are you sure that the question says "irrational fraction"? such usage is
quite unusual.

However lets try:

sqrt(125)/sqrt(5) = sqrt(5*25)/sqrt(5) = [sqrt(25) sqrt(5)] / sqrt(5) = sqrt(25) = 5.

RonL
• Mar 17th 2007, 02:44 AM
CaptainBlack
Don't make multiple posts of the same question, it confuses the system and wastes the helper time.

RonL
• Mar 17th 2007, 02:40 PM
mini
hi i think thats correct if it can be a surd over a surd can u explain how u got it

thanks
• Mar 17th 2007, 02:55 PM
CaptainBlack
Quote:

Originally Posted by mini
hi i think thats correct if it can be a surd over a surd can u explain how u got it

thanks

Well I needed two surds one of which was 5 times the other, so anything
like 5 sqrt(n) and sqrt(n) will do, Now 5 sqrt(n) = sqrt(25 n), so now we
choose any n and sqrt(25 n)/sqrt(n) will do the trick, as long as n is not a
perfect square when the numerator and denominator will be integers -
which we do not want.

RonL
• Mar 17th 2007, 06:43 PM
mini
thanks for your help but square root125/ square root 5 is a rational number it has to be irrational
• Mar 18th 2007, 02:48 AM
CaptainBlack
Quote:

Originally Posted by mini
thanks for your help but square root125/ square root 5 is a rational number it has to be irrational

No it has to be rational when all reduced to lowest form, as it has to
be 5, which is an integer but may be written 5/1 so is rational.

What you want is for both the numerator and denominator to be irrational,
as sqrt(125) and sqrt(5) are.

(there is no irrational number equal to 5)

RonL
• Mar 21st 2007, 03:48 PM
mini
ok thanks for your help you might be able to help with my other question the heading is money and investment thnkyou heaps and heaps