cos result incorrect

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+3 Q:

cos result incorrect

I import "math.h".

I can use the cos function, but when I execute cos(0.321139585333178) the result is 0.948876

If I use the calculator in Mac or use a normal calculator, the result is 0.999984292347418

Can anyone help me to solve that problem?

+19 A:

You're confusing degrees with radians.

cos(0.321139585333178 degrees) = 0.999984292

cos(0.321139585333178 radians) = 0.948876326

To convert from radians to degrees, multiply by 180/π.
To convert from degrees to radians, multiply by π/180.

Mark Byers 2010-06-14 07:06:32

Backwards. It should be "multiply by 180/π", "divide by 180/π"

Matthew Flaschen 2010-06-14 07:58:49

@Matthew Flaschen: +1 well spotted. It's amusing because I was going to work out the conversion myself but decided that there was a small risk I'd get it backwards so instead I decided to copy it from Wikipedia which is of course peer reviewed and for such a simple thing must be correct. http://en.wikipedia.org/wiki/Radian#Conversions . I will be more careful in future. ;)

Mark Byers 2010-06-14 08:10:20

@Matthew Flaschen: I see you have now fixed it in Wikipedia. :)

Mark Byers 2010-06-14 08:17:05

@Mark, and warned the vandal, and semi-protected it. :)

Matthew Flaschen 2010-06-14 08:25:58

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