Normal Vector from Two Vectors of Plane

Formula

$n=v_1\times v_2$

Example

With $v_1=(1,2,3)$ With $v_2=(2,1,-1)$ Find the normal vector $n$

Soln

$$n=v_1\times v_2=\left[\begin{array}{ccc}i& j& k\\ 1& 2& 3\\ 2& 1& -1\end{array}\right]=(-5,7,-3)$$