Equation of the plane passing through the line of intersection of the two planes r→⋅n→1=q1 and
r→⋅n→2=q2 and parallel to the line of intersection of r→⋅n→3=q3 and r→⋅n→4=q4 is
dependent on n→1⋅n→3
dependent on n→3⋅n→4
independent of q1 and q2
independent of q3 and q4
Equation of the required plane is
r¯⋅n¯1−q1+λr¯⋅n¯2−q2=0⇒r¯⋅n¯1+λn2−=q1+λq2 Now, perpendicular to n¯3×n¯4⇒n¯1+λn¯2⋅n¯3×n¯4=0
So independent on q3 and q4 only.