I'm looking for a proof of the following theorem:
If P1 written as : $A = px + qy + rz +d = 0$ and P2 written as $B = p'x + q'y + r'z + d' = 0$
All the planes going through the line intersection of P1 and P2 can be written as: $$A+mB = 0$$ It means that the plane A + mB = 0 and P1 and P2 have the same line intersection.