Planar vector angle online calculator

\(|a|=√[x1^2+y1^2]\)

\(|b|=√[x2^2+y2^2]\)

\(a \times b=(x1,y1)(x2,y2)=x1x2+y1y2\)

\(cos=a \times b/[|a| \times |b|] =(x1x2+y1y2)/[√[x1^2+y1^2] \times √[x2^2+y2^2]]\)