Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
Okay thanks a lot everyone. Bernard On 9/20/05, Kent Johnson <[EMAIL PROTECTED]> wrote: > Bernard Lebel wrote: > > Hello, > > > > I have this little math problem. I have this formula from wich I get a > > dot product between two vectors. > > > > cos(ß) = A.B / |A|.|B| = -0.0634 > > So this would give me radians, right? > > No, it's the cosine of ß, which has no units (a cosine is a ratio of two > lengths) > > > > > Then if I use > > > > math.degrees( -0.0634 ) > > > > This gives me a value of -3.6325524211294193. > > > > However I have a book in front of me who says I should get a value of > > 93.635 degrees. m > > > > Btw, in the book, the equation is written > > > > ß = cos-1(-0.0634) = 93.635, where -1 is actually an exponent. Maybe > > I'm just interpreting this wrong? > > The -1 means inverse. You have cos(ß) = -0.0634 - you want to find the angle > whose cosine is -0.0634, i.e. (inverse cosine)(-0.0634). Another name for > cos-1 is arccosine. In Python it is math.acos(): > >>> import math > >>> math.acos(-0.0634) > 1.6342388771557625 > >>> math.degrees(_) > 93.634990377223801 > > Kent > > > > > > > > Thanks > > Bernard > > ___ > > Tutor maillist - Tutor@python.org > > http://mail.python.org/mailman/listinfo/tutor > > > > > > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
On Tue, 20 Sep 2005, R. Alan Monroe wrote: > > >>> math.degrees(_) <--- in all my time on tutor > I have never noticed > this underscore trick > before That *is* cool. I've usually done something like: >>> a+ 3*b +(5*ht/9) * 32 9936254.2 Then use the up-arrow key to get >>> a+ 3*b +(5*ht/9) * 32 and edit it toL >>> x = a+ 3*b +(5*ht/9) * 32 >>> foo(x) The underscore's a nice stepsaver. And limiting it to the interpreter avoids perlish abuse. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
John Fouhy wrote: > On 21/09/05, R. Alan Monroe <[EMAIL PROTECTED]> wrote: > >>> >>> math.degrees(_) <--- in all my time on tutor >> >> I have never noticed >> this underscore trick >> before > > > I'm not a big fan of it, actually. It smells of Perl and those opaque > one-liners that make use of implicit functions implicitely setting > implicit variables... I'm actually not much of a fan either - it's too easy to lose what I wanted by doing another step, then it's too late. And I usually don't use it on tutor because I think it is a bit obscure. This time I wondered if anyone would notice :-) Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
John Fouhy wrote: > On 21/09/05, R. Alan Monroe <[EMAIL PROTECTED]> wrote: > >>> >>> math.degrees(_) <--- in all my time on tutor >> >> I have never noticed >> this underscore trick >> before > > > I'm not a big fan of it, actually. It smells of Perl and those opaque > one-liners that make use of implicit functions implicitely setting > implicit variables... > It also only works in *interactive* interpreters. -- Poor Yorick ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
On 21/09/05, R. Alan Monroe <[EMAIL PROTECTED]> wrote: > > >>> math.degrees(_) <--- in all my time on tutor > I have never noticed > this underscore trick > before I'm not a big fan of it, actually. It smells of Perl and those opaque one-liners that make use of implicit functions implicitely setting implicit variables... -- John. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
> Bernard Lebel wrote: > >>> import math > >>> math.acos(-0.0634) > 1.6342388771557625 > >>> math.degrees(_) <--- in all my time on tutor I have never noticed this underscore trick before > 93.634990377223801 That's quite handy. Alan ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Maths: getting degrees from radians (or am I wrong?)
Bernard Lebel wrote: > Hello, > > I have this little math problem. I have this formula from wich I get a > dot product between two vectors. > > cos(ß) = A.B / |A|.|B| = -0.0634 > So this would give me radians, right? No, it's the cosine of ß, which has no units (a cosine is a ratio of two lengths) > > Then if I use > > math.degrees( -0.0634 ) > > This gives me a value of -3.6325524211294193. > > However I have a book in front of me who says I should get a value of > 93.635 degrees. m > > Btw, in the book, the equation is written > > ß = cos-1(-0.0634) = 93.635, where -1 is actually an exponent. Maybe > I'm just interpreting this wrong? The -1 means inverse. You have cos(ß) = -0.0634 - you want to find the angle whose cosine is -0.0634, i.e. (inverse cosine)(-0.0634). Another name for cos-1 is arccosine. In Python it is math.acos(): >>> import math >>> math.acos(-0.0634) 1.6342388771557625 >>> math.degrees(_) 93.634990377223801 Kent > > > > Thanks > Bernard > ___ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > > ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Maths: getting degrees from radians (or am I wrong?)
Hello, I have this little math problem. I have this formula from wich I get a dot product between two vectors. cos(ß) = A.B / |A|.|B| = -0.0634 So this would give me radians, right? Then if I use math.degrees( -0.0634 ) This gives me a value of -3.6325524211294193. However I have a book in front of me who says I should get a value of 93.635 degrees. m Btw, in the book, the equation is written ß = cos-1(-0.0634) = 93.635, where -1 is actually an exponent. Maybe I'm just interpreting this wrong? Thanks Bernard ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
