Can you convert a decimal to a radical in simplest form?

• June 19th 2009, 06:11 PM
dschutte
Can you convert a decimal to a radical in simplest form?
Hello,

Can you help me find how to convert a decimal number to a radical (not rational) in simplest form? I need the answer with the check mark in it. ;^) For example, 3(check mark)5 = 6.70820394. But, how do you get that in reverse if you only know the decimal answer?

Otherwise, do you know of an online calculator or solver, or something like the TI-83 Graphing Calculator that would convert this?

Thanks,
Dan

PS
This seems to be essential for pre-calc, calc, and trig problems, but I haven't found an answer after several hours of searching on the Internet. Thanks for the help.
• June 19th 2009, 07:25 PM
mr fantastic
Quote:

Originally Posted by dschutte
Hello,

Can you help me find how to convert a decimal number to a radical (not rational) in simplest form? I need the answer with the check mark in it. ;^) For example, 3(check mark)5 = 6.70820394. But, how do you get that in reverse if you only know the decimal answer?

Otherwise, do you know of an online calculator or solver, or something like the TI-83 Graphing Calculator that would convert this?

Thanks,
Dan

PS
This seems to be essential for pre-calc, calc, and trig problems, but I haven't found an answer after several hours of searching on the Internet. Thanks for the help.

What does "3(check mark)5" mean?
• June 19th 2009, 07:33 PM
dschutte
It's 3(square root symbol, aka radical)5.
• June 19th 2009, 07:45 PM
malaygoel
simply square the decimal expression....you will get an integer.

In you example, you will get 45...so the radical experssion will be
$\sqrt{45}=\sqrt{3^25}=3\sqrt{5}$

if the square is...say 120...then the radical expression will be
$\sqrt{120}=\sqrt{2^230}=2\sqrt{30}$
• June 20th 2009, 02:45 PM
dschutte
Thanks Malay. Wow, that's actually really simple. When I Googled my question, others where asking also, but no seemed to know how to explain a simple answer. You rock, thanks a million!! (Clapping)
• June 20th 2009, 03:50 PM
skeeter
note that this technique of squaring only works if the decimal representation was calculated from the square root function of the calculator.

just typing in the decimal representation and squaring will, at best, get you a number close to an integer if the square root is irrational.

of course, it also helps to know that the decimal is the result of a square root ... could be a cube, fourth, fifth root ... etc.
• June 20th 2009, 10:20 PM
CaptainBlack
Quote:

Originally Posted by dschutte
Hello,

Can you help me find how to convert a decimal number to a radical (not rational) in simplest form? I need the answer with the check mark in it. ;^) For example, 3(check mark)5 = 6.70820394. But, how do you get that in reverse if you only know the decimal answer?

Otherwise, do you know of an online calculator or solver, or something like the TI-83 Graphing Calculator that would convert this?

Thanks,
Dan

PS
This seems to be essential for pre-calc, calc, and trig problems, but I haven't found an answer after several hours of searching on the Internet. Thanks for the help.

$3\sqrt{5} = 6.70820394$

is incorrectly rounded.

Removing the last digit (or correcting it) and feeding the number into the inverse symbolic calculator gives:

http://www.mathhelpforum.com/math-he...re714-gash.png

CB
• June 21st 2009, 09:09 PM
dschutte
Thanks Captain Black! I think that "Inverse Calculator" might be just the thing I've been searching for. I found it at http://glooscap.cs.dal.ca:8087/standard