What two lines are coplanar?

Answer 1

Two lines are coplanar if they both have 2 points in the same plane. So in an X,Y,Z

grid, one slope, be it X Y or Z, must be the same for both lines. To find the slope,

use Y1-Y2/X1-X2 or replace one of those values with Z. For this particular example,

it doesn't matter which is on the numerator, because it is a comparison.

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Short-cut:

Two lines that intersect are always coplanar.