1. ## Equation of plane.

Find the equation of the plane which passes through the points A(-1,-3,1), B(1,-2,0) and C(2,1,-1).
Calculate the shortest distance between the plane and the origin of the coordinate system.

2. Since A, B, and C lie in the plane, the vectors

$\overline{AB}=[2,1,-1]$

and $\overline{AC}=[3,4,-1]$ are parallel to the plane.

Therefore, $\overline{AB}\times \overline{AC}=\begin{vmatrix}i&j&k\\2&1&-1\\3&4&-1\end{vmatrix}$

$=2i+j+5k$

is normal to the plane, since it is perpendicular to $\overline{AB}, \;\ and \;\ \overline{AC}$.

By using the normal and the point (-1,-3,1) in the plane, we get the

point-normal form:

$2(x+1)+(y+3)+5(z-1)$

$2x+y+5z=0$

To find the distance between a point and a plane, use the formula:

$D=\frac{|ax_{0}+by_{0}+cz_{0}+d|}{\sqrt{a^{2}+b^{2 }+c^{2}}}$