1, two straight lines are parallel and have the same angle;

2. The two straight lines are parallel and the internal dislocation angles are equal;

3. Two straight lines are parallel and complementary.

Judgement theorem of parallel lines;

1, the same angle is equal, and two straight lines are parallel;

2. The internal dislocation angles are equal and the two straight lines are parallel;

3. The internal angles on the same side are complementary and the two straight lines are parallel;

4. Two straight lines are perpendicular to the third straight line at the same time, and the two straight lines are parallel.

Inference of parallel axioms;

If both lines are parallel to the third line, then the two lines are parallel to each other.