Originally Posted by

**M.R** Hi,

I am trying to solve the following problem:

1. Find the projection of $\displaystyle u=2i+j+3k$ on $\displaystyle v=-i+3j+2k$. Hence resolve $\displaystyle u$ into two vectors, one parallel to $\displaystyle v$ and the other perpendicular to $\displaystyle v$.

I can solve the the first part, just by using the projection formula = $\displaystyle (u . v / |v|) . v / |v|$

But how do I get it perpendicular to $\displaystyle v$? I know that if the dot product of two vectors = 0, then they are perpendicular. So:

projection dot ??? = 0. How do I calculate what to dot it with?