
Plane (geometry)
The question goes like this
Find the equation of the plane containing the lines through the origin with direction cosines proportional to 2,1,2 and 5,2,3.
I have done most of the part,but got confused on this part
I got two equations
5a+2b3c=0
2a+b2c=0
I just don't know how to apply cross multiplication for a,b and c.

$\displaystyle \left {\begin{array}{rrr} i & j & k \\ 5 & 2 & {  3} \\
2 & 1 & {  2} \\ \end{array} } \right = i\left {\begin{array}{rr}
2 & {  3} \\ 1 & {  3} \\ \end{array} } \right  j\left {\begin{array}{rr} 5 & {  3} \\ 2 & {  2} \\ \end{array} } \right + k\left {\begin{array}{rr} 5 & 2 \\ 2 & 1 \\ \end{array} } \right$
Now can you finish?