Question

Determinati masura, in radiani, a unghiului format din vectorii u=i+2j, v=2i-j.

Answer 1

U*v=(i+2j)(2i-j)=2i²-2j²=2-2=0  unde   i²=j²=1  si  i*j=0
u*v=0  =>   vectorii   sunt   perpendiculari dec <(u,v)=90 grade

Answer 2

u*v= 1*2+2*(-1)=0
cos ∡(u,v)=$\frac{u*v}{|u|*|v|}= \frac{0}{|u|*|v|}=0$
⇒ ∡(u,v)= pi/2