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+2b-3c=0

2a+b-2c=0

I just don't know how to apply cross multiplication for a,b and c.