#v.dot_product(w)=abs(v)*abs(w)*cos(theta), find theta!
v=vector([4,-3])
w=vector([2,5])
d=v.dot_product(w)
show(d)
show(d/abs(v)/abs(w))
show((arccos(d/abs(v)/abs(w))).n())
show((arccos(d/abs(v)/abs(w))*180/pi).n())
v1=plot(v)
w1=plot(w)
show(v1+w1,aspect_ratio=1)