If ` vec aa n d vec b` are two vectors and angle between them is `theta,` then `| vec axx vec b|^2+( vec adot vec b)^2=| vec a|^2| vec b|^2` `| vec axx vec b|=( vec adot vec b),iftheta=pi//4` ` vec axx vec b=( vec adot vec b) hat n ,(w h e r e hat n` is unit vector,`)` if `theta=pi//4` `( vec axx vec b)dot( vec a+ vec b)=0`