Cosine of 30?
September 24, 2010 7:50 AM   Subscribe

this isn't homework filter, I promise: what is the cosine of 30?
posted by pipti to Science & Nature (16 answers total)
 
http://www.wolframalpha.com/input/?i=cosine+of+30
posted by Busmick at 7:52 AM on September 24, 2010 [1 favorite]


Google
posted by rubbish bin night at 7:52 AM on September 24, 2010 [3 favorites]


cosine(30) = 0.15425145
For future reference, you can simply type a math equation into Google and get an answer.
posted by carmicha at 7:53 AM on September 24, 2010 [1 favorite]


You need to specify the units... 30 what?

According to the calculator in Windows XP:

Cosine(30 radians) = 0.15425144988758405071866214661421
Cosine(30 grads) = 0.89100652418836786235970957141363
Cosine(30 degrees) = 0.86602540378443864676372317075294

According to Google Cosine(30) = 0.15425145(which agrees with the radian number above).
posted by MikeWarot at 7:57 AM on September 24, 2010 [1 favorite]


Interestingly, Google is assuming 30 radians, while Worlfram picked degrees, hence the difference, and hence the inherit risk in blindly trusting Google. 30 degrees is a much more reasonable assumption so go with wolfram. Also they have the exact answer instead of the decimal approximation.

Also, google "cosine 30 degrees" to get the right answer.
posted by PercussivePaul at 7:57 AM on September 24, 2010 [1 favorite]


Cosine of 30° or cosine of 30 radians? These are two pretty different answers.

cosine(30°)= sqrt(3)/2, or about 0.866
posted by muddgirl at 7:58 AM on September 24, 2010


Be careful! I'm guessing you want the cosine of 30 degrees, not the cosine of 30 radians, which Google is giving you.

The sine of 30 degrees is 0.5, so the cosine is sqrt(0.75), since sine squared plus cosine squared equals one.
posted by ecurtz at 8:00 AM on September 24, 2010


Is it in degrees or radians? If it is in degrees then it is sqrt(3)/2 if it is in radians then carmicha's answer.
This is because of soh-cah-toa Cosine = adjacent over hypotenuse. A 30-60-90 triangle has a hypotenuse of 2 and short side of 1 and a middle length side of sqrt(3). The 30 is adjacent to the middle and the hypotenuse so sqrt(3) over 2.
posted by koolkat at 8:01 AM on September 24, 2010


Hold on a second. 30 doesn't have a cosine. Cosines apply to angles.
Wolfram guesses you mean 30 degrees if you ask it for cos(30) but Google guesses you mean 30 radians.

You can make Google work in degrees too: cosine(30 degrees) = 0.866025404
posted by doiheartwentyone at 8:02 AM on September 24, 2010


or, what everyone else said.
posted by doiheartwentyone at 8:03 AM on September 24, 2010


Response by poster: Sorry--this is for a friend. We did google it and got two different answers; thus I turned to the green. We have solved the problem. thank you! It was for an architectural puzzle.
posted by pipti at 8:03 AM on September 24, 2010


If you meant 30 degrees, cos(30 degrees) = sqrt(3)/2 ~ 0.866.
posted by lukemeister at 8:16 AM on September 24, 2010


Hold on a second. 30 doesn't have a cosine. Cosines apply to angles.

The convention in angular functions is that the units are radians. Degrees should have that little dot. Radians and Degrees are ratios and thus are dimensionless. They are different because Degrees are normalized. So, yes, 30 does have a cosine.
posted by vacapinta at 8:45 AM on September 24, 2010 [1 favorite]


Cosines apply to angles.

In addition to vacapinta's point, this is just plain wrong. Take, for example, simple harmonic motion (e.g., "mass on a spring" as the classic example)—it's expressed as a trigonometric function, and yet no angles are involved. Cosines and sines show up all over the place in math and physics, even when there are no angles.
posted by DevilsAdvocate at 8:57 AM on September 24, 2010


Indeed, the domain of the cosine function is all real numbers. By that token, any real number "has a cosine."
posted by King Bee at 9:38 AM on September 24, 2010


There's also the complex-valued cosine function, whose domain is any complex number. So, in that sense, pretty much any number you could possibly think of "has a cosine".
posted by King Bee at 9:40 AM on September 24, 2010


« Older Found booze, what to do?   |   Write What You Know? Newer »
This thread is closed to new comments.