Line in a plane
Plane in 3D space is uniquelly given by:
3 non collinear points 
2 intersecting lines 
2 parallel lines; line an point 
Remember that if two lines intersect, they have a single point in common, and that point must project from view to view. This property is very usefull for construction of missing view of object in the plane.
2 intersecting lines
2 parallel lines; line an point
Remember that if two lines intersect, they have a single point in common, and that point must project from view to view. This property is very usefull for construction of missing view of object in the plane.
GeoGebra 4035
Plane α is given by two intersecting lines a, b. Construct the front view of line m in the plane α =(a, b).
Trace lines of the planes are intersection line of the given plane and the drowing frontal and horizontal planes. Trace lines provides pictorial representation of the plane convinient for many contructions, e.g. intersection with other objects, determining the tru size.