Did you get a response yet?
On Sun, 2005-30-10 at 13:14 -0800, Fred J. wrote:
> I am trying to figure the angle between vector and
> getting some un-expected answers
>
> (%i114) magnitude(x) := sqrt(x.x)$
>
> (%i115) a:[1,0]$ b:[0,1]$ c:[1,2]$
> d:[sqrt(2),sqrt(7)]$
>
> (%i119) acos((a.b)/(magnitude(a)*magnitude(b)));
> (%o119) %pi/2 <---- expected
>
> (%i120) acos((c.d)/(magnitude(c)*magnitude(d)));
>
> (%i122) acos((c.d)/(magnitude(c)*magnitude(d)));
> (%o122) acos((2*sqrt(7)+sqrt(2))/(3*sqrt(5))) <--
> pi/??
I'm not a Maxima expert but I know that Maxima likes to keep exact
results and so the output here is the best it can do. You can get a
decimal approximation with
(%i) acos((c.d)/(magnitude(c)*magnitude(d))),numer;
but will get the result below, ie 0.0272350692885.
> does it need to be hand written in-order to get a
> answer?
>
>
> (%i124) e:2*sqrt(7) + sqrt(2) ,numer;
> (%o125) 6.705716184502276
>
> (%i126) 3*sqrt(5) ,numer;
> (%o126) 6.708203932499369
>
> (%i127) acos(%o125/%o126);
> (%o127) 0.0272350692885 <--- even now, where is the
> radians answer
This is the radian answer. Your angle is very small, have a look at
plot2d([[parametric,t,2*t,[t,0,1]],[parametric,sqrt(2)*t,sqrt(7)*t,[t,0,1]]],[x,0,3]);
and you will see a very small angle. Why do you think it is not a radian
result?
:-) Bob
--
Dr. Robert J. Jerrard, Professor of Mathematics,
Concordia University College of Alberta,
7128 Ada Blvd., Edmonton, Alberta, T5B 4E4, Canada.
Phone: (780) 479-9291, Fax: (780) 474-1933.