To Construct a Line That Intersects a Line Segment at the Active Angle

Select the Construct Line at Active Angle tool (Drawing > Home > Placement > Place Multi-line split button).
Select the element to intersect.
If the Method is From Point, this data point defines the intersection.
Enter a data point.
If Length is off, this data point defines the length.

If the Method is To Point, this data point defines the intersection.

Construct Line at Active Angle (AA denotes the Active Angle). Top Left: Method: From Point Length not constrained. Top Right: Method: To Point Length not constrained. Bottom Left: Method: From Point Length constrained. Bottom Right: Method: To Point Length constrained.