Question

Question #38c69

Answer 1

A line `d` is always contained in a plane.

Either `d` is contained in a plane parrallel to the plane `alpha`, and then `d nn alpha = O/`.

Or `d` is contained in a plan `beta` that is not parallel to `alpha`, in that case `beta nn alpha = gamma` where `gamma` is a line, and `gamma nn d != O/`, which means the 2 lines intercept in 1 point, and this point is included in the plane `alpha`. I hope you understood, don't hesitate to ask.