3D line plane intersection, with simple plane

Question

i have two points in 3D space which have X-coordinates with different signum. so one of them lies definitely on one side of the X-plane and one on the other.

now i w

Answer 1

P1 = (x1,y1,z1)
P2 = (x2,y2,z2)

k1 = -x2/(x1-x2)
k2 = 1-k1

Intersection = k1*P1 + k2*P2    or:
Ix = 0              - we know this one
Iy = k1*y1 + k2*y2
Iz = k1*z1 + k2*z2

I'm assuming P1 is to the right and P2 to the left. It may work with them reversed.